Bruce,

Perhaps the unwanted effects of the shaking can be reduced with a change in control setup and use. I'm thinking, adjust rates to give only enough throw needed to fly around, like a gentle trainer. Use only a modest amount of exponential to smooth out center stick reactivity. Too much expo creates over sensitivity at high stick deflections. I recommend this in general anyway. Many modelers have way too much throw in their setups. Take the setup as far "soft feel" as you can for your friend. Make full aileron just enough to do a modest roll. Make full elevator just enough to do a lazy loop and flair for landing.

You might also try having him use a transmitter tray. Add extended length control sticks to give even larger range of motion. And crank the stick return spring tension all the way up. Maybe even add stiffer return springs. Have him fly by holding the ends of the sticks between thumb and forefinger.

Basically if you can't stop the shaking, reduce the problem it causes. He probably has reduced feel/perception of the stick movements he's making. All this should improve that too.

Hope this helps?

Multiflyer