Don't give him the choice. Get rid of them in front of him and show him that the cups are the only thing available. If he cries for a bottle, tough luck. He's going to have to cry. The crying won't last forever, and when he realizes you're not giving in, he'll stop.
A child his age can't conceptualize "When you're 3 we're taking the bottle away." If you don't want him to have them now, then take them away now. If you're willing to let him manipulate you and keep using them until he's 3, then just let him have them. Warning him that you're going to take the bottle away without actually taking it away is stressful for him. He's got very limited concept on what the future means, because all he's interested in is the present.
Therefore YOU have to be consistent and you can't expect a 2 1/2 yr old to make the decision for you. Some children have no problem transitioning completely, but others, like your son, need to have the decision made for them.