+1, I did not even think of that, hmmmm.
Use your tube cutter & just rock it back and forth until you punch thru to make the slit, and to make it wider just go a bit deeper. I drilled a small piece of wood(1/2") and stuck the tubing thru the hole to hold it in the vise while I worked the cutter back and forth. The wood crushed holding the tubing , nice clean job. Cheers