I have cut a few more cup holders into my boat. I used blue painters tape and a dremmel.
I taped up the area with the blue tape, and then traced the holes onto the tape. I then used the dremmel to cut into the dash and trace the circle. I slowly enlarged the holes until they where just right - enough tension to keep the cup holders in place without needing to glue them.
I put a shop vac's hose underneath while I was cutting to help suck in some of the dust.