J.Y.
I agree that he is probably hungry. Could you leave him a cup of milk next to his bed for him to drink at 1am? If you place it there when you go to bed, and it is in an insulated cup, it should stay cold enough. Hopefully full fat milk will fill him enough to make it to morning. And if it easily accessible, maybe he won't wake you. It sounds like water with a splash of milk doesn't fill him so he is awake again so soon.
Also, FYI, incarnation instant breakfast comes in lactose and soy free. One of my foster children drank it. I had to order it though as I couldn't find it in stores.