For clarification, the hole saw drill bit is the same thing you use to drill holes in doors for locksets. Makes a perfectly round hole. Here's a link to a similar hole saw.
They come in all sizes, the one I used drilled a hole approximately the size of a doorknob. Just make sure you drill a pilot hole first, and be patient, you want cut the plastic, not melt it.
you sir are a genius! (or I'm just an idiot...)