There have been a few threads about getting BF babies to take a bottle. we had some success with DS but only from DH - not SIL who has him for 4 hours a week (he screamed when she produced the bottle).
Last night we finally gave the doidy cup a try with some room temp EBM. Instead of screams we had giggles and a DS reaching for the cup. Today SIL gave it a try and send me a picture - now in my profile - while I was at work.
I have o idea how much milk he's actually drunk, but so log as he's happy while I'm out, I don't care - he can catch up when I'm back.