Originally Posted by
ericoseveins
intrigued by the one suggestion of welding a nut to the sheared bolt.
It's a standard auto mechanic technique, possibly less effective on the 5 mm threads a bike mechanic has to remove. If you don't get good fusion pretty much as soon as you strike an arc you're just getting it hot, so be sure you're aiming at a good clean bit of bolt, and with adequate current. Welding a washer first helps with smaller bolts, because you're not obstructed by a nut so you can see your arc, and work on some sort of bead, rather than just point and hope.