Will the holes need to be covered with screen or anything to stop escapees?
I use a drill, with a small drill bit. I smooth the pieces down that are caused by the drill, but it works well.
You just make the holes tiny, like about 1/8" and make lots of them. You can use a drill, but it's a pain in the butt to smooth down all the little holes (rough edges can cut the snakie snouts). In my experience, the melting is so much easier, although monotonous and time consuming when you're doing 18 baby bins!