I just posted some pictures of my install of the Vista Cruise universal model, was around $35 (I overpaid, had to have it now,got it at a honda dealer most stock them) on the gallery, There under Greg Mines pics. I was able to fit the clamp under the plastic and mount the crossbar with a little Dremel mod. I didn't like the position of the finger lock I had seen on someone else's pics on the forum. It was just to awkward to turn on and off for me. I have used it for over two months now and it works great. Forget the oring idea, just to dangerous for me. When I need to brake in a hurry I don't want the throttle stuck on.
Start with carefully pulling apart the handle bar plastics close to the brake reservoir, loosen the brake reservoir clamp screw and slide it over enough to fit the clamp next to it, Its a little tricky getting the clamp screws in but it can be done.
Just be careful with the Dremel, there's part of the plastic that keeps the handle bar cover together just under were I cut into the plastic towards the top. Look at the pictures and start with a small hole in the middle where I cut through, don't go to deep, look through with a flashlight, cut a little at a time until you open it up enough to just fit the crossbar through to were it mounts on the clamp.With a little time and effort it can look like a factory install. Another thing worth mentioning, it does take away from some real estate on the grip (approx. 5/16") but not that much.
Sorry but I don't know how to attach the pics to a message yet.
Hope this helps someone, be glad to answer any questions. Greg