I introduced the bottle to my first 3 children at the same age.
Some kids just won't have it.
My 3rd child absolutely refused the bottle, and NEVER took one. I flew my mom out here from Colorado and left him with her for 8 hours when he was nearly 7 months! He wouldn't take a bottle ALL DAY. I, too, was gearing up to return to work. So, I left him with the home care provider 3 part-time days in one week to see if she could coerce him (thinking that he could still smell my milk in the house with my mom). He still wouldn't have it, even though I was pumping my breast milk. He was eating some solids, so he wasn't screaming all day or anything - but once he saw me, it was ATTACK. I tried EIGHT different nipples! Oh, joy!
Anyway, I trained him on the cup, and put my pumped milk in a sippy cup. I was fortunate to work nearby, and went on my lunch break to nurse him. I nursed in the morning, pumped at 10 am, nursed at lunch, pumped at 3pm, nursed before dinner and at bedtime.
So, try working the cup in there - and if you can manage a lunchtime feeding, go for it. Good luck.
My fourth child is 5 months, and I won't be returning to work until he is 1 year old - so, I've decided to skip the bottle routine altogether with this child. But I have introduced the cup already with my breastmilk in it. I thicken it with a bit of cereal so it doesn't drip down his face.
Congrats! If you can transition slowly by doing a couple of days a week and add one day until a full week, it may help your son get the picture. Blessings to you!