I'm guessing he doesn't have access to weights either? (Judging from your other post, about yourself) That'll make it a little more difficult. Bodyweight exercises are fine up to a point. But once you can do more than 10 reps or so, it's not challenging enough to stimulate muscle growth.
If there's no chance of scoring a cheap, local gym membership (which might not help anyway, since most places require you to be 16 or 17...doesn't that just figure), I'd say look into getting whatever equipment you can, on your own. Pool your money together and try to find a cheap Olympic weight set (should be about $150, for 300 pounds of total weight and 1 barbell).
That's the first step, and really all you need for a barebones, hardcore, starter's routine. If that's not an option, he can find resistance tubing for 5 or 10 bucks, and that'll let him do all sorts of basic movements.
Just as important as training, though, will be his eating. He wants to focus on standard issue "clean" eating: Whole grains breads, all kinds of veggies (yes, vegetables...tough it out), all kinds of fruits, chicken, turkey, red meat (roast beef sandwiches...yay!!), whole eggs, whole milk, peanut butter, things like that.
If he doesn't eat at least 4 meals a day, give him a dead leg. That should motivate him to eat. (Okay, I was kidding about the dead leg. Bros shouldn't fight...this coming from a guy who had his collarbone broken by his older sister, okay.)