What I thought I would do when I did my ,,,heated grips with Symtec units and new BMW grips is this.
Being a machinist, I was going to start by cutting the grips flange and a bit of the grip off exposing the throttle tube. I would then turn up a spacer that would fill the gap between the tube and the ID of the Breakaway. I would not use the rubber bit they give you to go over the grip. I would then cut the part I turned up in two making two half moons. Slip those in the gap, tighten the set screws and call it good. I think this has a fighting chance of being a smooth install. The first time I put it on over some grips that I had to butcher at NatSTOC, didn't go so well. I got it, but it was a lot of messing around to get it tweaked to allow free throttle snap-back.