I have a jig I built out of an old roller skate wheels { the metal ones}. I welded a circular collar onto the front of the skate wheel frame off center about 2" and use a section of 1/8"x2" flat stock as the guide track, it isn;t pretty like a manufacturer would sell but it cost about $6 plus the flat bar so total out of pocket was about $20. This setup still depends on the operators hand travel speed to be accurate for a consistant weld.
Hope this helps,
It's impossible to make anything 'idiot proof' because then they will only make better idiots. (I know 'cause I am one)
John's comment on the Bug-O equipment is the same thought that comes to my mind. We have used several types of Bug-Os, (the stitch welder, Uni-bugs, and others) with good success. The Uni-bug can travel vertical-upwards, and can also follow a reasonable radius if desired.
It clamps on an edge of a bar, angle, beam flange or whatever.
We have used ours with FCAW guns, plasma torches, and oxy-fuel torches.
We have also used the Airco type of track burners (turtles) the same way. There are lots of ways to securely clamp a Bernard or other type of gun to the equipment. We made up a toggle switch in parallel to the trigger switch, so that it allows triggering the wire into position then snap on the toggle for continuous running.
Not sure all that is what you were looking for but maybe it will spark an idea for you.
Chet Guilford