A couple of things that might help are some method of raising the bar position, a couple of ways to do that are:
GenMar Riser plates
Reaper Risers
Helibars
Also, you could lower the seat to shift your position a little up and back, this can be done with a shaved seat from any number of sources - one of the more popular here is the Tobin seat, but that is by no means the only version.
I have seen grips that are oversized and/or have foam - they could help, but you may also want to invest in a throttle lock - enables you to give your throttle hand a little rest (away from traffic anyway) - there are a couple of throttle locking methods available such as the vista lock and the thottlemeister bar ends (I am partial to these)
Anyway, just a few suggestiond for a start in your research, if you are curious, I have 1/2 in reaper risers, a Tobin seat and heavy polished Throttlemeisters on Bessie...