I personally would not put him on a puppy food. I'm not a fan of puppy food for puppies, so I would suggest feeding him 1/4-1/2 cup more food every day. If he doesn't gain weight that way, you can add Satin Balls into his meal.
http://www.njboxers.com/satin-balls-recipe.htm
If you're worried about raw meat, you can lightly cook them to enhance their aroma and flavor.