2 of my previous cars...
So I've done this sort of thing before
Molding it on isn't exactly a good idea, concidering the bumper and lip are both made of very soft flexable materials. It would just be a matter of time before the paint would crack. If both the bumper and the lip were made of glassfiber, it would work better 'cause there wouldn't be as much movement in the materials.
I'll use what I've always used: the same glue that's used for gluing on your car windows. It's better than what most people use (sikaflex), bonds better, and it's elastic enough. But it's not recomended for anyone who're planning to remove the styling - 'cause once it's on, it's ON!
But I have no need to remove it. And hearing people use double sided tape is THE dumbest shit. That's just begging for your styling to fall off
Anyways - thanks for the heads up! Anything constructive is always appriciated.