If it were me, I'd just drill it out. Get a good metal bit, about half the diameter of that bolt, and drill right through the middle. Then grab your vice graps, give a little twist, and it should come right out. Just be sure not to drill too deep if there is anything behind the bolt, and if there is, just use one of the other bolts to judge how deep to go. Also, be careful to drill straight through so you don't hose up the threaded hole.