Re-learning the potty training rules

It's been a while since I've been in the realm of potty training. Over four years as a matter of fact, so I'm pretty out of practice. The older kids were functioning toilet users well before their third birthday, and I figured Dalin would follow suit especially since he was showing such an intrest six months ago. I was wrong. His birthday came and went and he was still pretty attached to the diapers. I told Dalin that we weren't buying any more diapers and he was nervously watching as they dwindled away. This is how the conversation went last week when he realized he was using the last diaper.

D: I don't want to be potty trained (the very fact he knows that phrase was a sure sign we were way over due)
Me: I'm sorry, but the lady at the store won't let three-year-olds buy diapers (not really a lie because I'm sure no respectable store clerk would do any sort of transaction with a three-year-old)
D: I don't want to be three anymore.
Me: Okay then you have to give all the presents back that you got for your birthday, do you want to do that?
D: No

One day he was wearing some spiderman underpants, and in an effort to motivate him to keep them dry I told him not to pee on spiderman. So later when he had an accident I said, "I thought you were going to keep spiderman dry." To which he replied, "I didn't pee on spiderman, I peed on Doc-Oc, he's a bad guy." There goes that tactic. We are only a week into the serious training and fortunately for me he's doing pretty well and having little to no accidents. Now we just have to work on number two.