Hi S.,
I just went through this with my 11m old. He wouldn't take anything out of a sippy cup at all. It may be the cup - at this point my son is weaned off the bottle completely, drinking whole milk, but we had to try several different types of sippy cups before we found one he would take. He still will only drink out of the "tossable" sippy cups.
Like nipples and bottles, there are differences and maybe he just doesn't like the one you're offering. I'd try a different brand/style - some have hard sips, some soft so try the opposite of what you've been trying so far.
Persistence and patience. Keep trying at every meal, and perhaps try juice or water as an alternative first. My son first drank Gerber garden juice out of a sippy cup. Only after that would he reluctantly drink formula from it.
L.