Since you said smaller than a dime, you might try a piece of brass tubing sharpened on the inside (take an X-acto, insert it in the tube, and spin the inside edge against the blade)... I'm thinking this might work since you mentioned thinner gauge styrene type plastic. You could even heat the tube up and "hot-knife" it to cut it easier(like the old days of hot-knifing plastic models.. ha).. just a few thoughts there. Other then that, I like the punch idea too. Good luck.