Repro direct connection trunk lid spoiler- any ideas on mounting without drilling?

That'll look nice, this may be a day late and a dollar short but, if you use the fiberglass foot idea which is a good one, use epoxy resin in lieu of methyl methacrylate or vinyl ester ( boat resin). Most epoxies won't cure as fast but they shrink far less. When repairing fiberglass ALWAYS use epoxy for this reason. Boat resins consume up to half of their bond strength in shrinkage. I agree with Tru Blu's 3m tape idea, epoxies are tenacious bonders however, once hard the bond line can be shocked with impact whereas a 3m tape type product bonds tenaciously and has a ton of flexural strength.