I don't understand, can't you just put the old stem back in, reinsert the old bolt til its just snug and then back it off several turns, whack the top of the bolt with a hammer to loosen the wedge and then remove the whole assembly?
I'm confused what you mean by the expander bolt is stuck in there. You can only remove the stem if you either loosen the wedge and remove the wedge/bolt/stem as an assembly or you remove the bolt completely leaving the wedge still in the neck and then remove the stem.