How old is he?
There was the trip that my then 8-yo was afraid to ride Everest and RnRC; he thought he wanted to, but he was afraid to go. He also wanted a certain soccer jersey from a shop in Epcot that was $50, but he didn't want to spend his own money to get it. DH told him we would buy the jersey if he rode both rides, and he did. He is 13 now and still loves those rides! We've also done the "everyone rides once and if you don't like it, you don't ever have to ride it again" with things like HM or MS that aren't really scary--this applies to me as well, I'm a chicken. The same DS as above has ridden Splash twice and doesn't like it at all. He goes through the line with us and takes the chicken exit if we are waiting standby, or just waits for us somewhere if we use FP.
My youngest DS was the same way with ToT. He was only 4 though, and we weren't going to bribe him at that age for something that might scare him. We were getting ready to leave DHS one evening, and he asked what we were going to do now because he didn't want to go back to the room. DH told him that the two of them were going to go ride ToT by themselves, and he said OK, and off they went! I was nervous for him because I had never ridden ToT at that time, but he loved it! They ended up riding twice in a row with only a 10-minute wait!