What type of a program are you going to put him on? That would help a lot.
Me for example, I am trying to stay as lean as possible while gaining mass. So in a situation but I am sitting around 4500-5000 calories and have put on size but leanness is still there. I am using Isotean as the only non-food source after workouts, otherwise all whole food. Of course an athletic multi, fish oils, creatine ect. Essentially the staples for supplements.