Re: Rejecting Bottle
My daughter did this too. How long are you planning on being away from your son? If it's for a date night, just a few hours? Or do you plan on longer separations?
What my babysitter did was just offer the bottle often and if Lilah cried, M just removed it. Then she would try again later. I am away from her for 10.5 hours four days a week though, so she really had to drink milk in some way.
In your case I don't think it's imperative that your son take the bottle because you are at home with him during the day and it doesn't seem like you are talking about leaving for long periods of time. I think you could nurse him right before you leave and then when you get back. Leave a bottle with the caregiver and if he doesn't take it, he doesn't take it.
If you're uncomfortable with that, you could try a sippy or straw cup. Or what about making a milk slushie - partially frozen milk and they could give it to him on a spoon. Is he interested in drinking out of a regular cup? M also poured milk into Lilah's mouth when she was refusing bottles just to make sure she got some milk in her.
Other people have tried different bottle/nipple combinations to make it work. Does your son take a pacifier? If so, maybe a nipple shaped the same as the paci? Something else to try if you haven't already - switch to a fast flow nipple. If it's only a once in a while thing, I don't think he's going to develop a bottle preference at 6 months. We switched to a fast flow just to get some milk into my babies mouth, and 8 or 9 months later we're going strong - she has grown to accept bottles but does not like them.
Lilah 10/08 nursed 25 months
Beatrix 01/11 nursed 30 months