Assuming its a M10 XZN head bolt and that you've stripped out the head before you go crazy on it you should try these"

http://www.sjdiscounttools.com/irw53227.html

You can use the largest one that will barely fit, pound it into the stripped hole and maybe get it out that way. They don't always work but when they do it saves a lot of other work to get to the happy ending. The other style with internal flutes which fit outside the bolt head also work good if you can get them onto the bolt head.

Using a small pencil type torch to direct heat onto the damaged bolt head just before you apply force to it is a good technique, you don't need it red hot or anything like that, "too hot to touch" might give you just enough elongation to make things possible under these bad circumstances.

I've never had or heard of someone stripping out one of these bolt heads who was being careful and using a high quality tool!