Its not hard to gain weight. Dude is 6'7", Hell be able to gain weight. Just like anything else it simply takes consistency and frequency of food and workouts. Unless he has a rare medical disorder the only scientific thing he has to do is take in more energy then he burns. Its not rocket science.
Eh... I beg to differ. There are a lot of hard gainers out there with sky high metabolisms. (I was one)
You would also be surprised at the amount of HS kids I train that all they want to do is add bulk for college or Varsity level sports. All of them have incredibly high metabolisms and eat more food than I can imagine. They are also on a very strict workout regime. And it's very difficult for them to gain weight. Also remember, the more muscle mass they add, the higher their metabolism will get.
That being said: I'm not saying this kid will have a hard time gaining weight because I don't know him and what his metabolic levels are. However, to say it's as easy as just lifting weights and eating a lot of food is ignorant.
I'm sure our staff will have him on a very strict diet and training routine to gain as much weight and muscle mass as possible, though.