Get him to cut out ALL caffeine. The withdrawals will be massive if he's a regular consumer and it might take a week or two to get a result but worth trying.

Also, when I have trouble sleeping, I find deep breathing helps best out of everything. Breathe in for the count of five, hold for the count of five, exhale for the count of five, hold for the count of five before breathing in again. Keep doing this for as long as he can and then at least if he's not asleep he'll be relaxed LOL.