I'm not sure why it is important to have a child drink whole milk. Although he is not having a reaction that you can see, and appears to be "tolerating" it, something is not right. He may well be having a reaction internally - just because he isn't throwing up or getting a rash doesn't mean he is allergy-free. He is refusing it no matter how you try to disguise it. I think you should go with that and not try to force it. I once heard someone say that the purpose of whole cow's milk is to turn a 100 pound calf into a 600 pound steer in 6 months! My son never did well with milk products, and he got a lot healthier after we stopped trying to work it into his diet. He is now 18 and a star athlete, and has hardly ever been to the doctor except for regular check-ups.
If you are worried about nutrition, and feel he needs to get off formula, why not try a patented product like Reliv's Now for Kids? It's dairy free, has every nutrient in the right balance that kids need, and is produced by one of the most highly rated companies - see Forbes, Fortune, Business Week and Success From Home magazines, also DeMarche and the Direct Selling Association. There are lots of people you can talk to to get their personal success stories - any Reliv distributor will make sure you get that info. Not only do kids get excellent nutrition, they almost always get phenomenal results with overall health, little or no illness (including colds, strep, ear infections, etc.). Reliv works by supporting the immune system and by getting optimal nutrition to the cellular level - you give the body great fuel, and it knows what to do with it.
I would definitely look into it and give up the milk battle. It's not helping, and it may be hurting.
Let me know if you want more info on Reliv. It works! And it takes the guesswork out of nutrition. It was formulated by Dr. Carl Hastings, the world-renowned expert on nutrition who was behind ProSoBee and Enfamil formulas, so he knows his stuff! The company is highly ethical and has a fabulous humanitarian mission, feeding 41,000 people a day world-wide with top notch products. My family is on the adult products, and I can't tell you the fabulous results we have had in 5 months - reduced allergies, improved blood pressure and cholesterol, more energy and stamina, no illnesses, etc.
Good luck with whatever you decide!
D.