I may not have the tools necessary to smack the broken bolt out of the topmount, but I do have a big-ass ratchet set.
I went ahead and checked the other bolts for the front struts. They were easy enough to break loose, and I tightened them back down gently with a hand ratchet, so they should be fine. It looks like it was just the one.
I hadn't thought of that - I dunno if the sizes match up exactly, but after eyeballing them, I'd guess that we should be able to use a bolt off of the stock topmount as a temporary placeholder until I can get a replacement.
It's not like I'm gonna be racing any time soon