I had made small holes in some to allow wires to pass through. I used tubes of brass, and sharpened the tip like a round exacto and put it into my drill... worked great.

I'm sure you're looking for bigger than 1/4" diameter, but it's just my example to point out anything WITHOUT teeth and razor sharp will work well.

Maybe a copper tube from the hardware store? and file the INSIDE the the pipe sharp... I've hard no luck with conventional drill bits or hole saw bits into balsa sheet...

just my .02
hope it spurs some ideas for ya