Have you considered M3 RivNuts?
I've set M6 Riv-Nuts in Polycarbonate, Fibreglass and ABS by using a washer on the back and crimping tight enough to hold but not tight enough to damage, the hole in the base material is drilled clearance and it's the tension of the Riv-Nut between head and washer that holds by friction on the surfaces.

I used washers cut from Polyurethane sheet on both sides of the Polycarbonate and Fibreglass to prevent wear with vibration, rain and road dirt but I suspect you won't have those issues ;-)
Regards,
Nick