Back when I lived in the flatlands (MN and WI) I had a 600 XCR that I put motorcycle handlebars a twist grip throttle on; I absolutely loved it for trail riding. The guys at the local Polaris dealer (Duluth Lawn & Sport) thought I was crazy, probably still do. In fact if I was ever forced to live in the flatlands again I would do it again.
My thumb joint at the palm gets super sore from a flipper. Remember the days of pulling against the springs on 3 carburators?
Anyway when I went out west on vacation the twist grip was damn near impossible to control when you sidehill on the left side. It may a bit better now that I have learned how to sidehill better.
If you have $100 or so to experment with I say do it and report back.