C.
Have him pick out a potty seat. He might prefer a seat that just goes on the toilet rather a freestanding unit. If he picks it out, he might be more willing to give it a try.
Better bribes might work too. I went to walmart and picked out whole assortment of cheap toys like farm animals, crayons, playing cards and things. Also, if there is a favorite place to go like Chuck'e'Cheese, use that as a bribe. Go potty 5 times or 3 times and you can go.
My final suggestion would be if you are desperate enough, plan one week to be training week. Lock yourselves in rooms with hard floors and put your son in big boy underwear. Bring the potty in with you and make sure he can get to it quickly. Don't pressure him to use it though. Watch tv, do some activities, whatever he normally does throughout the day. He will probably wet himself a few times so have a supply of underwear and papertowels on hand. If you see him starting to go, move him on the potty as fast as possible. After a while he will figure it out. I used it and have heard of a few other people trying this method but you have to make sure the kid is really ready.