Use a utility knife. You cut a hole in the end very carefully! My buddy shaved one side of the hook so it would not interfer with the wires. I'm pretty sure the heating wires come up the outside of those bars. If you cut a wire your grips might not heat or cause other problems. I cut mine on my 99 mxz and the lights got shorted out when I used low beams!
I had to buy new heat elements for that side for about $22.