Okay, if you go to Home Depot (or any plumbing supply shop), look for 1/2" brass compression fitting inserts. They're these small brass rings, and are somewhat sharp on the edges. I just lay one on the grip tape, and give it a few taps with a hammer - watch your fingers. Cuts a nice hole.
They don't last long (brass is soft), but usually you get 3 or 4 in a package for well under a dollar, so who cares.
I'm sure there are better methods, but this works well for me.