Took down the bumpy texture with 50 grit on a DA, an orbital, and in some places by hand (that part sucked). Then went back over the whole thing with 100, then 150 grit until it was pretty smooth (not perfect, that would take forever!!!!). Then the secret weapon... adheasion promotor for plastic parts! Kinda like a solvent in a spray can. Got it a VatoZone. Goes on clear and then kinda dries up. Then hit it with a couple coates of high build primer. At this point, you could use some spot putty or bondo. But as you found out, bondo products just wont stick to the plastic.
After the primer was dry, 400grit wet/dry, a quick coat of primer/sealer then it was off to the paint booth (er, garage)
Whole thing actually turned out pretty good