Buy him a Ripstik to practice on at home. Better than a skateboard for learning torsional twist. If he can become proficient on a Ripstik the transition to snowboarding should be very quick.
Excellent, thanks, Grizz. That looks like it really hones the skill for torsional twist!
Just a thought...make a 6-8 inch plastic snowboard out of a milk carton or something to show him torsional steering; fore/aft weighting during phases of the turn, de-cambering the snowboard and engaging the sidecuts for turns; and using the idea of keeping your body parts inside the cereal box (the board being the bottom of the cereal box) to show how that effects balance and efficency.
Awesome idea, wrath. I think he's a visual learner, so that will be perfect. It will also satisfy my inner geek