Mike,
I believe what you are asking is how to change its characteristic from constant voltage to constant current?
I saw a link around here recently (equipment for sale?) that advertised a (single phase?) inverter weld power supply with slope sufficiently adjustable to be able to do that; it's nothing new or revolutionary as I believe you are aware, but I dont know of any single phase welders that hve the ability designed in to them. Are you considering adding that adjustment ability to your welder? It's undoubtedly at best impractical, as was previously suggested; someone who knows the Lincoln box itself would perhaps know what's involved.
Perhaps rephrase the question?
I can understand how flux core MIG does not equate with the advantages of SMAW you are looking for, but, as if cash grows on trees around here, the best recommendation will probably be to buy yet another welder that will do what you want. (there's some benefit from owning an auxillary welder as well)
If you dont NEED it and can get the filler you want in FC, all the better.
Regards,
D