The best mass gaining exercise is chewing. Focus on his diet first, then worry about training. Mostly though, all he’ll need is a program revolving around the big basics- squats, bench, deads, chins, rows etc. Keep the reps in the 8 to 12 range, which is the hypertrophy range for most people. Or he can just adopt any program from the T-mag site.
Like I said, I think the specific type of training you do in a mass program is secondary to diet- as long as he’s using free weights, skipping the cardio (or at least keeping it to a bare minimum), getting plenty of sleep and allowing adequate recovery time, he’ll do fine. Read my “Diet Manifesto” article for more info.