i had the same trouble when i had to give my daughter some formula when i went back
to work after 6 months. have you tried feeding the bottle to him while he is snugged right up to your breast? works best when your breasts are quite full and nearing a feed, so he can smell your milk. he will try to reach your breasts at first, but if you keep trying and dont give in by feeding him yourself it can work. i found this worked well as once she was used to me giving her the bottle, others could aswell, but she still new the smell of 'real' milk and could have both bottles and breast. ( is he does take the bottle from you when you are near feeding time, remember to express after or it may decrease your milk flow)