A few thoughts from my experience installing the G2 and heated grips on a 2010:
Post #20 in this thread does a great job of laying out the steps, however, the grips on my bike, a 2010, did not peel off as shown in the post. Each end, where the rubber contacts the throttle tube, the grip was essentially fused to the tube. There was no way to peel it off. I finally managed to get the heat element out, but it was not an easy process. You can see what the grip looked like when I was done.
I then tried to get too cute, and it bit me in the ass. I didn't want the two small wires routed externally without any protection. They are going to rub between the grip and throttle housing so I wanted to shrink tube them. So, I unsoldered them fromm the mylar heat element, stuck on some heat shrink tubing, and soldered them back - or so I thought. The connections looked good, but something went wrong and I didn't have a circuit. After a couple more attempts I had soldered through the mylar to the throttle body (good thing it's metal) and effectively trashed it. So there goes the OEM heat element.
Not to be easily defeated (after all, I had just destroyed a $171 heated grip), I bought a after market kit and using the wire connection from the destroyed OEM grip, I wired the aftermarket grip to the stock switch and it works. I was afraid that the new heat element would tirgger the CANBUS and power would be cut off. But it didn't and so now I have a heated, G2 throttle.
This pic shows what the wiring looks like from underneath.
The new heated grip does not get as hot as the left stock one. I'm sure that some of the issue is the thicker, ribbed grip I used. I'm going to try a thinner one and see if that makes a difference. Also, the grip heater I used had separate high and low input wires, and I used "low" (I was afraid of exceeding the limits imposed by the CANBUS. I never tested the high setting to see if it would work. I was getting tired of the project and was happy that low worked and just finished it.) Even though it's not as hot, I've used it several times now with temps in the low 40's (with Barkbusters) and my hands have stayed plenty warm.
Just to show that there a other ways to get this done, even if you screw up like me on the first attempt.