A better question might be "Has anyone not had this problem?"

You could try soaking in PBB for a few days/weeks, along with periodic beating on the curved part of the drum (staying away from the ribs). But I don't have a lot of faith in that approach.
Next level would be a "hand impact tool" and a BFH. Eg,
http://www.amazon.com/Lisle-29200-Hand-Impact-Tool/dp/B0002NYDRG plus
http://www.harborfreight.com/4-lb-sledge-hammer-with-hickory-handle-95129.html Be sure to replace the wheel bearings afterwards, since the impact may damage them and lead to rapid failure.
Last resort is a Dremel mototool with an abrasive cutoff blade or possibly a carbide burr. With care, you should be able to cut away enough of the screw head to get the drum off, without damaging the drum beyond use. With the drum out of the way, I found that the remains of the screw came out fairly easily.
Or you could just leave the screws out, since they don't seem to do anything useful. The wheel and lug nuts clamp the drum firmly in place when they are installed. Well, at least on cars with disc wheels or the splined adapters. Perhaps not on early TRs with the wire wheel hubs.