Epoxy?
3M makes 5200, which is a caulk/sealant that acts like a strong glue. That's probably a little bit too permanent for your purposes, it would be very tough to ever replace the molding.
Which silicone sealant did you use? 3M makes some that are not quite as strong, but might be stronger glues than what you used.
Actually, I would have tried one of the pressure sensitive glues, or contact cements. They come in different strengths. Like a caulk, they stay flexible.