Go subliminal!!!
Maybe you've tried this, but.... Have you gone to the store to let him pick out some "big boy pants" with a cartoon character on them that he really likes? If not, maybe try that. Bring them home and put them AWAY--but somewhere in HIS reach, like an end table drawer. Make a big deal about
the fact that you are putting them away for later, when he's ready. Every time he takes them out and asks to
open them up, simply say "Oh, let's put those away. Those are for when you go on the potty" or, "we have to save those for after you go on the potty". They will be right there under his nose and they just might get under his skin--if you know what I mean! If he shows no interest in them, set them out in plain sight so the conversation comes up every now and then. You essentially stop talking about
potty training unless HE brings it up, and I think he'll bring it up because those pants are soooo cool and they are right there under his nose...so tempting... Just a thought.....
If that doesn't work I would ignore the situation completely and not push him. It really sounds like you've tried everything! Lots of boys are around age 4 when they finally get it, so I wouldn't be too concerned.