I'm not sure why he needs milk. There are many other beverages that contain protein - try rice milk or soy milk. He can get calcium from other products such as yogurt. If he won't eat those, you could add a fantastic supplement called Now for Kids which has all the vitamins, minerals, trace elements, omega 3s and DHA for brain development. It comes in vanilla and chocolate and is delicious - you can put it in any liquid such as water, juice, milk. It was formulated by the same scientist who was on the team who developed ProSoBee infant formula and who is a world renowned expert in liquid nutrition. It's available from distributors - not in stores. I'd be happy to give you more info. This product also helps kids who have some lactose intolerance - not sure if that's what's going on with your son. It doesn't sound like he keeps the milk in him long enough to be uncomfortable, but I raise the issue just so you can consider it.