If you don't mind paraphenalia, I'd get him a small pipe or one hitter. With a one hitter, he could take a small hit of just herb. It will save him money, plus one tiny hit shouldn't mess him up, just help him out. I think this would be your best best. That way he can control how much he's smoking instead of just putting it all in a joint. My motto is "Additives are icky when you mix them with the sticky"