You could try cutting a flat head slot in it with a dremel or suchp. Don't go to deep in the head of the screw so you torque the head off but deep enough to get a good bite and make sure the screwdriver head fits snug In the slot. Use a nice fat flat head as close to the width of the screw head as possible. Or go to Sears and get a set of screw extractors, which sometimes don't work all that great but as far as that screw is concerned you've got nothing to lose. Drilling it out is a decent option. I've done it plenty of times on some odd shit. Just make sure your drill bit is the right size so you don't Fuck up the threads in the binding. I would pick a bit that fits in the rounded out area in the screw head and work up in size if need be. Remember as far as this type of thing is concerned (metals that is), you can remove material but you can't put it back as (far as the thread are concerned). A machine shop is also an option.
"If you dont live for something, you'll die for nothing"-Jasta