What we do is first sand the area with 400 grit wet/dry. Then we spray a coat of 3M 90 adhesive to the surface, and let it dry before applying the light. After that, we seal around the ends with E6000 clear sealer/adhesive. Then we tell the customer to remember to press the lights down several times over the first couple of weeks, and when they think of it. IF a spot gets loose, use the E6000 to re attach.

Since going to this method, no lights have been lost. Only over a period of 2-3 years though...