Hellgate
Wizard
I use a "Cramp Buster" all the time. This device features a tab that protrudes from the rear side of the grip. Positioning can be adjusted. After getting used to it, it minimizes the amount of torque needed to keep the throttle open. About $10.
And then on long trips, I occasionally use an N.E.P. throttle lock. It can be adjusted so that it is just tight enough to hold the throttle open. I find that by dropping the right hand down beside me for a minute every hour or so, will keep the circulation going better, and be less tiring. About $18.
I haven't done this, but with some talk about grip size, what about using the cushioned wrap material that is used on road bicycle handlebars? It stretches a little, so that when wrapped it stays tight, and could be used to substantially increase grip size, while adding padding to the grip. About $20.
Better cycling wrap is actually cork. I love the Cinelli brand. It lasts of years. Cinelli is about $19.95. The no name stuff is about $10.95, but it doesn't feel the same after a long ride.