Yes. TIG (tungsten inert Gas, or as the old timers called it heliArc, cause the thicker metals used helium in the gas for less cooling?)
TIG is sort of an electric version of brazing. So there is a filler rod that is melted into the weld joint. I just used solid coper wire and welded it into the alloy. I had about 10 cupcake pan ingots I used.
I got greedy and tried welding a #6 stranded wire into some lead. It didn't dilute enough, and the lead was liquefied and i ended up with a chunk of garbage on top. If the lead is molten, the copper floats, and you end up adding copper to copper.
A solid # 12 or 10 seemed to work best, and only a few inches at a time into solid alloy in a fresh spot, then let it cool and weld more into a new spot.
After you run out of fresh alloy surface, remelt all the ingots together and flux and stir good then pour fresh ingots and repeat till you get it all added.
I made a bunch of 4.0% Cu enriched ingots to spike my other alloy with.
I also tried placing a bunch of coiled wire in a stainless jar of alloy and cover the surface with powdered charcoal and put it in the wood burner surounded by hot coals till the jar was dull orange from heat, then stirred good and tossed in some wax.
That appeared to work, but it cooled a bit as i poured it off and ended up with a solid mass floating on top. I believe its antimony that separated out. Its brittle but appears to be a crystalline metal and must need a lot of heat to melt. (Web searh said almost 1200°F). So that may not be the best way to do it if it causes the antimony to separate out. Its fairly difficult to get it to dissolve back in without crushing it up and submerging it.
The TIG method seemed to work good if you only melt a bead of copper into a fresh area of alloy that is still solid.