If you broke it off tightening it, it will come out pretty easy. I have drilled a hole and hammered a masonry nail in the hole and removed bolts. I filed the end of the nail to look like a Philip's head and tapped it in a hole just a little deeper than a screw head and not quite as big as big as the nail end. I guess you can call it the poor man's easy out. It stamped slot that held up well enough to back the bolt out with my cordless drill and a screw driver bit. Granted the bolt was softer than the nail and the fan bolt may be harder but you shouldn't have to get to radical with it to get it out. I have also drilled a head bolt and used JB weld to glue a stud that I could get some vice grips on. In both cases they were not really stuck just broken to short to get a grip on. I do have a set of easy outs now and they are great.

Neil
http://community.webshots.com/user/neilhatten