No experience with these, but lots with plenty of other stripped BB's and many other things. If its plastic I would have already carefully ground out a small section so I could break it out without damaging the threads but being fully prepared to restore them as they will probably need that anyway. I have an air dremel like tool that with a burr can get in to very tight spots. Self made custom rethreader tools have never failed to resolve the aftermath.

This once again brings up the BB conundrum of not removing it for service until something goes wrong. This is a perfect example of that. Now you have more of a problem than you want. IMHO BB's should be completely disassembled whenever servicing any part of them. This especially includes driveside cup removal for thread service to help avoid problems like this later. I know many disagree on this and that is fine, I will always do it as a proper service so there are less of these posts.