Fixing broken/missing screw bosses on plastic parts

I'm trying to fix up a pair of 1970-1971 Duster tail light lenses and finding that a common issue is broken off screw bosses. I could put longer screws in to hold them on some places, but I'm wondering if anybody has had any luck with rebuilding the missing bosses? I've done some internet surfing and have found a number of products to repair cracked plastic but not to rebuild the bosses when missing. Hoping someone can point me in the right direction. Thanks!