LBS has tried and failed, so no ammount of plus gas, shock'n'unlock (which is nowhere near as cold as I remember it being, changed recipie?) or bench vices are going to help.
Frame is a Ron Cooper road frame, lugges and Columbus steel tubing (basic CrMo though, nothing fancy)
a) heat, applied to the seatpost untill it's close to melting to break the bond with the frame? Would try the frame but woried I'd melt the bronze and not wanting to try twisting it while it'd hot.
b) chemicals? Caustic should dissolve aluminium, but how to keep it in the frame untill all traces of aluminium are removed? I've not got a big enough tank or enough caustic to dip the whole thing! Ammonia should work too, but a bit more unplesant and the same issues?
c) crush the seatpost in a vice just above the clamp and hope ti pulls away from the seatube rather than crack?