big pointed punch and a big hammer would be what id be doing or, beating on a stud extractor like this: http://img.directindustry.com/images...s-g/P24143.jpg
beat it on as straight and as far down as you can then turn it with a breaker bar. once your crack the bolt off go forwards half a turn then back half a turn just to get the thread going agian then just undo it all the way. best tool i ever bought was a set of these.