Happens a lot. I would say that if song and dance ain't working, I'd cut the song and dance, and go as laidback as you can on it. I've been in childcare for 10 years (next week!) and I think that's half the secret - we've seen SO many kids TTd that it's just not a big deal anymore, so we're far mroe relaxed about it, and then so are the kids.
Like a bit of "well, here's a nappy, and here's your blue jocks and your red jocks. You decide which ones you're going to wear." When he goes for the jocks, say "well, that's a good choice. remember that you'll have to do your wees and poos int he toilet if you are wearing jocks."
Rather than forcing the toilet, I would say "Do you need to go to the toilet? Remember that you're wearing jocks and you'll need to do your wees and poos in the toilet" If he's good at telling you, that's a great sign.
If he hasn't been for two hours, and you're worried, ask him to go. If he says no, give him a bit of "OK, well, do you want to go later? How many minutes? Maybe... 10?" Let him think he's the boss, and gets to choose how many minutes.
I've seen lollies work. You start off with one lolly for every toilet success, then later you move on to a lolly for every day without an accident. Eventually, they all seem to just get on with it.

Shrug off any accidents. Really, in the scheme of things, they don't matter. Say, very matter of factly "Next time you can remember to use the toilet." and move on, swiftly, don't mention it again.
If you're getting a lot of accidents, and you suspect it's because he's reluctant to leave his play, make sure he takes full responsibility for the accidents. Make him take off the wet clothes, put them in the machine, put on the new ones (I usually cut help right back to a bare minimum at this point) so that he learns that it's actually MORE time consuming to wet your pants than go to the toilet. Most kids figure this out pretty quick.

Also, don't be surprised if he regresses when number 2 comes along. Lots of kids do it.

Hope that's helpful!