my car was being tuned by power engineering years ago and my cam belt was deemed lose so they tightened it and snapped one of my bolts off and left me to my own devices to get it home(it goes without saying i never used them again).

The way me and my mate got it out was to take the tensioner off and there was a little stub sticking out of the block so we kept dropping bits of weld onto it till it built up and undone it with mole grips, hope this makes sense and good luck