Once you have a hole drilled in the problem bolt, one of the easiest things to do is to drive the square tang of a file into the hole and use an adjustable wrench to turn the file to unscrew the remaining part of the bolt. I've done this in the last year in my own garage. It's an old Italian bike mechanic's trick. No special tools, no wasted time (if you have a file the right size) and you get to post about it in places like this.