The picture above shows a RubberMaid plastic dinner plate.  Note the off center hole that has been carved out with the utility (carpet) knife shown to the left of the plate.  If such a knife has a sharp point you can just position the knife point on the plate and twist it back and forth with some downward pressure and a small hole will be formed.  A power drill can be used to make the hole but the plate must be very firmly secured when doing so for it is easy to crack the plate.