Saw a slot into the bolt head and remove it with a screwdriver if you've given up conservative solutions already. Trouble is, then you're losing that spacer barrel thigy... So you should try hammering an imperial allen bit, a torx bit or a screwdriver of slightly too large size into that motherlover. My pick would be a one size too large torx bit, filed slightly to a wedge shape. Pick something that almost fits, bash it in w/ a big hammer and turn.

Actually, yeah. I couldn't quite resign myself to taking a dremel to my bike (I have until this afternoon) so I mixed up some more JB Weld and coated and pouded in (gently, it is a hub after all...) the next larger non-metric size. I'm going to wait until around 2 or so to try it out, just to make sure it has plenty of time...

Fingers crossed.