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Welcome Ian!
I have a couple of questions for you.
(1) What make is the inverter? (2) Have you called the manufacturer of the inverter to ask the same question?
Now, here's my two cents worth. (warning: this might take some time!)
Inversion is the opposite of rectification. Rectification is the conversion of alternating current into direct current, and is achieved using rectifiers or diodes, example: four diodes or SCR's in a bridge connection for single phase, and six for three-phase input.
Inversion converts direct current into alternating current. However, an inverter is not simply a device like a diode, but a network of MANY components designed to achieve this conversion.
The great majority of arc welding today uses direct current, and since the mains(input) are invariably alternating current, some method is required for changing from AC to DC. Inversion is only part of what happens within the inverter power source. Many other electronic and electrical conversions and transformations are required to convert the mains(input) supply into one suitable for welding.
Now let's get into inverter design and operation. This design is used to explain the principles involved in the operation of welding inverter circuits and not to be confused as the only design used in industry today. This is why it is important to contact the mfgr. of the inverter in order to find out if you can do what you mentioned, and to find out if warranty issues can play a role in your decision to move further.
The inverter is an electronic network for converting DC to AC, and the frequency of the current must be increased from that of 60 Hz(Hertz)coming from the mains to up to around 60kHz.
It has been proven that increasing the frequency gives more controllable and adjustable qualities since it is easier to change electronic circuits than to vary large inductances made of iron and copper.
First the incoming mains are passed into a rectifier which converts AC to DC. In order to improve the power factor of the power source a large filter capacitor immediately follows the rectifier stage. This has the advantage of providing a fast response energy store (the mains supply is relatively slow). Then the inverter circuit converts the incoming DC obtained from mains (input) frequency (60Hz) to square wave AC again but, at a much higher frequency than that of the mains supply. This AC at high frequency is passed into a transformer bringing down the voltage and increasing the current to that used in a welding circuit. The electricity is again rectified to DC, and passed through the filter inductor where, by Lenz's law, it is smoothed before passing to the welding terminals for connection to the electrode or GTAW(TIG) torch.
Many units today have a DC or AC(HF) output. This type of power source may have "back to back" or "push -pull" connection of more than one inverter, but that depends on the arrangement. (you should be able to figure out the difference between "back to back and "push-pull" as it relates to parallel and series connection.)
This is perhaps the simplest and most common: The DC welding output is connected to a network of four high-current semi-conductor switches (thyristors or transistors) in a "bridge network". The "switches" are switched on and off in pairs, 1 and 3 together, or 2 and 4 together, by a timing circuit. The output is AC(HF), the current square wave, suitable for welding aluminum, and this network is a further form of inversion.
In Summary: In an inverter-based power source, the incoming mains or input at 60Hz (50Hz in europe) is first rectified to DC before being fed to the inverter circuit. This circuit then reconverts the DC supply to an AC supply, but at a much higher frequency than that of the mains(input) with ranges of 6-60kHz depending on the "brand". Since the "input transformer is now operating at a high frequency, it's size and weight are greatly reduced compared with that required at 60Hz. The high frequency transformers use cores of ferrite, not iron laminations, and after transformation to the correct voltage, and current levels, the high frequency AC is again rectified to DC, and supplied to a welding output "smoothing" inductor filter, the size, and weight of which is also reduced because of the high frequency.
Machines offering DC and AC output generally incorporate an inverter/commutator circuit immediately before the output terminals. The inverters use either frequency modulation or pulse width modulation(PWM) as the means of control. Current and voltage feedback signals from the welding output are used within the cloed-loop control systems to maintain the required welding parameters. By varying the electronic controls or software as in the case of microprocessor-based controls, it's possible to provide machines with both static, and dynamic characteristics for a wide range of welding processes (SMAW, GTAW, GMAW, FCAW, pulsed or not etc.).
Inverters are characterized by their small size, and low weight compared with conventional machines, and offer high efficiency and high power factor. Their flexability, fast response, and excellent welding properties will extend their use over the coming years.
This information was quoted in part from: "The Science and practice of Welding" Volume 1 "Welding science and technology" 10th edition, by A.C. Davies, published by Cambridge University Press.
Now that I read your question again, I think by reading how the AC(HF) is produced within the power source just before the output(welding) terminals, you may have a problem with regards to preventing high frequency feedback into the internal control circuits or microprocessor if you do'nt consider a method of preventing this possibility. I maybe incorrect in this assumption because I do'nt know which brand of inverter power source you are using, and do not have the schematics available for your inverter in order to determine this possibility. Losing your warranty would be a shame also. So, I think it's best to contact the manufacturer's technical support division in order to find out further as to whether or not you can do what you had in mind. I hope that the excerpts from the quoted book and myself have been able to explain how inverter power sources work in order to guide you in the right direction.
Respectfully,
SSBN727 Run Silent... Run Deep!!!