I've got an animal jumpoff remix with a stuck, broken pinch bolt. The (hollow) bolt snapped in half after the friend I got it from over tightened the rear of the stem. both pinch bolts broke, but one before the other. To make up for the missing bolt, which he was able to remove, he overtightened the lower one, and, yeah. Anyway, i removed the back/unheaded half with a pair of pliers. However, I've tried removing the head of the bolt with an allen wrench, and the bolt spins, but doesn't move. How can I get it out?