I'm not trying to bond wood to styrofoam, I'd like to bond styrofoam to styrofoam.
I designed a 'spreader' type mount for my lights. The idea is to install two spreaders per fixture inside the ceiling. The spreaders will make contact with the wood veneer of the ceiling, and then two bolts pull the fixture up until the desired tension is achieved. MUCH, MUCH better than the existing drywall screws lightly screwed directly to the foam.
If anyone is interested, I've attached an STL file so you guys can print your own. You'll have to remove the '.wav' extension to make the file usable.