drinking milk?

its a pain but put the milk in a soy milk container, or in a regular container. he doesnt have to know. after even a month of him drinking it just fine with no complaints, then stop the pooring it into another container and you then can rightfully make him sit there and drink it because you will know 100% it is just him being stubborn. i mean, you still have a right to, but you will also then have more proof doing it this way. 

my step dad wont eat generic cereal, so cereal is always placed in a container so he doesnt know its generic and eats it just fine. i know its kinda different, but sometimes you just gotta trick those boys !

you could also get chocolate protein powder to make chocolate milk? its much healthier than even olvoltine. just use enough to make it chocolatey, not the serving amount (its way to much for me and i love chocolate milk)

 Have you tried almond milk?  Coconut milk?  Rice milk?

I put chocolate flavored pediasure in my dd's milk.  Like 1 part chocolate pediasure and 3 parts regular milk.  Its chocolate but packed with vitamins so its good for em'.

 i was raised on goats milk and our dd was raised on acidopholous milk due to lactose intolerance. i found lactaid pills makes milk tolerable for me in small quantities.

I would have made the switch my mixing cups half and half (half silk half milk)... then i would cut that down 1/4 silk 3/4 milk.. and do that until it turns to straight milk!

Why not get ovaltine or something that is fairly healthy but chocolately as well.

Humans do not need to drink milk. We can get calcium from many other sources. I would not be concerned at all.