I know y'all probably think this is cheating, but it works for me! Have you
tried the "Ready Prongs?" I think Stuller sells them. They are different size
circles of white and yellow gold with solder underneath them. I dip the piece
in my alcohol / boric acid mixture. Have the little prong ready and a wet
flux brush right there. Light the ring on fire and as soon as it cools, get
the prong tip wet with flux and stick it on the warm ring right where you want
it. It should stay put while you solder it in place. Sometimes you need to
follow up with a little hard solder. Clean up with brown or blue wheel.
If your prong is missing altogether, disregard the above message and use
prongwire and a third hand.
Hoping I won't get laughed off orchid,