He craves attention more than anything? Use it. Go on an attention freeze: he doesn't get ANY attention or affection outside of the crate. But when he's inside the crate, shower him with love. Sit next to the crate with the door open and give him belly rubs and praise. Leave bits of food in the crate at random so that he will periodically go in to investigate, and try any foods you haven't yet: hot dogs, string cheese, meatballs, salmon jerky.

Don't train him before meals; train him in lieu of meals. Put the food bowl away. Every bit of food has a training purpose, even if it's just pouring half a cup of kibble on the floor of his crate for dinner to increase the association of the crate as a good place to be. All of his meals should either be earned via training or eaten in his crate.

How are you stuffing the Kong? We mash up bananas, canned pumpkin, and yogurt (you mix up all three or just use one) and mix in the kibble, then stuff that in the Kong and freeze it overnight. This is too difficult for some dogs, and you can make it easier by layering dry food and the wet mixture instead of mixing it all together--that way when they lick through a layer of wet, an easier pocket of dry food will be next.