Right or wrong, I did it my way.
I had thought about using the blow in foam inside the bars, but the hook inserts went in so far, the foam would not have done much good.
Once I opened the RSI extended grip heater instructions (big gasp I know) I noticed in the mice-type that these were not to be mounted over the mounting hole for bar hooks. Can someone explain this knowledge to me, I don't know how you attach the bar hooks without the recessed bolt hole. You can tell that since my bars were cut down, the extended heaters would go almost to the ends of the bars now either requiring me to return these and settle for shorter heaters, or do something not on the instructions. Anyway, I have the heaters now, because I ride with my hands out on the hooks so I wanted heat out there. I measured the recess pockets and they are exactly .5" so I rummage around and find a .5" dowel and cut it to fit in each recess. If I need to take them out later I can insert a screw in the dowel and pull out. I added cork on the right side to bring the surface up flush but left the left one as bare wood since it was close to the surface of the cork. I installed the grip heaters but the plastic membrane was not overly pliable so I used the heat gun to soften it up a little to mold to the bar. This was all fine and dandy but I was concerned that I would bugger up the heater trying to get the RSI grips on over the top. I didn't like the idea of using electrical tape as the heat from the heaters may make the tape adhesive runny and make for slippery grips. In came the 1" shrink tube that I have on hand. Slid it on, shrunk it down and then cut the wrinkle off that develops on the inside of the curl of each bar hook. Once that is secured, I used some air and blew the grips on. Sealed the end of the heater where the wires come up with some liquid electrical tape to help keep the wires stationary in their new home.
With the 1/16" cork and the added layer of shrink tube, these are thicker than stock grips but I like that better for my big hands. Also with the shrink tube, I think I can change the grips out more regularly without damaging the heater, or so I hope.
Hope they work.