I think you're going to have to drill the broken bolt piece out of the hole, but good luck with that because if I remember right, it's a rather tight space to work in. Once you get the bolt out, if the threads are striped, your best bet is to try to tap a new, slightly larger, set of threads and then use a little bit bigger bolt. That's the only way I can think of to fix it. I'm sorry to hear you had this problem though... sounds like somewhat of a freak accident. Good luck!
07 WRX (Albins 5MT + Blouch 20G)
Jorge Carrillo Tuned (365 whp/340 wtq)