I'll be honest with you-- some babies just never do. I started working again when DS was four months old, and he never would take a bottle. He would happily starve while he waited for me again. We tried a zillion different types of bottles, in every possible position and situation, and he never would take any of them. What we wound up having to do is to syringe his milk into him, slowly and arduously, until he was old enough to eat from a spoon, and then we started freezing the milk until it was slushy and spooning it into him.
Other non-bottle feeding options--
a medicine dropper
a tiny medicine cup
a supplemental-nurser (SNS) tube taped to a finger or pacifier
No matter which way you do it, though, it's painfully slow and requires a lot of patience to keep baby taking enough to stay hydrated and maintain adequate growth. What I wound up doing after awhile was reducing my hours to very part-time and taking the pay cut, in order to stay and nurse him, because his growth slowed down a lot.