Hi J.,
I would say never to offer the bottle yourself, and to try to have the same person offer the bottle. The fact is that your son can either accept the bottle now or when you are at work, it doesn't really matter. When you are at work, he will evenutally get the idea that if he wants to eat, he will need to have a bottle. It would be wrong to deny a baby food simply to get them to take a bottle.
I'd suggest when the bottle is offered, to make sure the caregiver warms the nipple as well as the bottle, and to smear a little EBM on the nipple so the baby immediately knows the smell and taste is familiar
My son's first day at daycare, he took one bottle of EBM, the 2nd day he took two, and the third day, he took three which was his normal intake.
Good luck