Acetone will soften fiberglass, be careful.
As will normal paint stripper.
But used very carefully, paint stripper is what I would use - leave it just long enough to soften the paint (the start of bubbling?) but not long enough to reach the fiberglass underneath.
You would need to buy plenty as the first experiments will involve wiping it off before it has done its job - too short a time (not softened the paint) is a much better outcome than too long a time (damaged the fiberglass), so expect to do most areas more than once.