I don't know if it would work here, but sometimes you can find a different screw which will 'bite' the remaining plastic (FRP) well enough to hold. Look for different thread pitches in the same size first; this seems to work best. Look for SAE or Metric screws that are slightly larger next (again with various thread pitches} next. And don't overlook wood screws which vary wildly in diameter as there's no precision standards set for these.
Do be very careful here or you may split the plastic! Such a screw could be cut to protrude just enough to be turned with pliers, as cutting a slot in something this small would be more than most of us could easily do.
If someone happens to have access to a metric thread pitch gauge and can measure that, or who knows that spec already, we might be able to find a source for thin nuts (perhaps meant for panel switch mounting etc) more cheaply than those made and sold for lens rings. Anything "specialty" always costs more but often a substitute can function equally well. Just thinking aloud here
Phil