Hi M.,
Since I am only on baby #1 so far, and she took to a sippy cup at 4 mos trying to copy my tea drinking, my suggestion may not work, but here it is.
Have you tried putting a drink in either cup of something you know he will drink in a bottle or a regular cup. Our daughter grabbed for our cup, so we would hold the cup of water for her, and still do, as she "laps" up the water with her tongue. But she realized she could control the cup if she drank from a sippy cup--so she loves the idea that she can drink from both M & D's cups but she really loves the idea that SHE is control of her own drinking. My friend's son went from breast directly to a grown up plastic cup, skipped bottle and sippy cup.
Control may be the issue--he is not sure if he is ready to be in control or he wants to participate in what you are drinking. In our household we don't drink juice and we both hate soda, so she can have breast milk, formula milk, chammomile or peppermint tea or water. Normally, she gets cold to lukewarm tea or ice water since she is a big fan of freezing her teething gums.
Not sure if this is helpful or not, but you may have to really think out of the box and see if there are other issues surrounding why he won't drink from the things you have offered him.
L.