If he hasn't started preschool yet I would wait until then so you can speak to them and they can help. He might be inspired when most of the other children are using the toilets (they're also generally smaller which is much more appealing!)
If you have a potty I would leave it out near where you change him all the time, and I would encourage nappy off time in not potty training ways - for eg you could get the paddling pool out and pretend to be out of swim nappies.
Hi This is not a lot of help but I'm in the same boat with my DS 3.2 yr old, he is big for his age but no were ready to pt. he is one that LOVES!!!! having poo in his nappy, tells me he likes the warm squishy feeling, he used to fight me tooth and nail to stay in a pooey one but now I leave him in it until he is more agreeable. He will happily play in his room for quite some time before coming to me asking to be changed, then with no fights or battling him. I'm hoping he will start to dislike the poo feeling soon as his cloth nappies are just *&% well you can just imagine !! haha
I showed my son the video on YouTube about poo land. I told him that the poo needs to go back to it's mummy and daddy. Then we bribed him with goldfish!! He was so pleased to go and get Goldie and ginger when he did poo in his potty.