Getting a ceased screw out of fiberglass??

Thanks! It's a lift spoiler. I'll get photos up once I get a chance.

My real worry is that the screws will break off, not so much stripping the heads. I need a way to break them loose without breaking the screw. All 4 screws broke off that connected it to the trunk when being removed. I swear it couldn't have been more than 2 pound foot. They practically fell apart, and those weren't rusted!!!