He probably needs more stick tension in the radio so he has a better feel for what he's doing. If he has any hand shaking issues a transmitter tray and switching to the pinch method will probably help him with that. For the original question, I'd definitely have him look into the Eagle Tree unit. This is not a guy who is going to try and compete in aerobatics or take the hobby to the nth degree. At his age, he just wants to get some fresh air and enjoy the time playing with airplanes. That's exactly the kind of pilot that the stability systems were made for, and with his physical limitations it will probably mean the difference between soloing and being a safe pilot on his own or remaining on the buddy box forever.