The way a heatsink on the back will mainly help is by getting rid of what little heat does get deposited in to the PCB. As we know, their are prickly little pins sticking out the back side of the PCB where the ZIF socket resides. You need something thick, buildable, thermal conductive, and non-electrically conductive, that will adhere the heatsink one. JB weld (also called cold weld) comes to mind. It is a thick two part resign that you will find at automotive stores. I'm not sure if conducts electricity or not. But It's worth testing. Just buy some, mix a little up, role it in to a ball, let it harden, then test it with a multi-meter set to the continuity beeper. If it passes, I'd use it.