More pics and a rusty bolt removal question after gap

I can't get the rear finder spats off because the bolts holding them on have rusted into place. The rust has turned the threads into junk and rounded off the nuts. I can't heat the stuff because the fiberglass melts and grease catches on fire (I've tried). Ideas? I'd rather not destroy the things because I don't have replacements.

Yes I wear flip-flops while working. I would be bare foot but I didn't want blue all over my feet.