What type of inflammation are you hoping to treat him for? I have seen a couple other people give MSM for arthritis. I used to give an arthritic cat a powder than contained MSM and glucosamine chondroitin, and a few other things I think. With Neko, who had even worse arthritis, I started using Duralactin for her inflammation. It's not good for cats who can't handle milk or who have high calcium values, but definitely helped her. Worth having a discussion with the vet if you think of trying it.
For supplements, what works here is putting mixing them in with part of a Churu.