It sounds like surgery is the only other option if he can't take the other things. There are quite a few young people who have had the j-pouch done over on the ostomy board (one little boy was 5). It sounds like a scary and awful for your child to have to go through this, but the ones who have had it done all have said they are so glad to have their lives back and are sorry they didn't do it earlier. If he is really sick, you don't want him to have to suffer through these very important years. Come on over to the ostomy board when you are ready.
What does his GI say? Even with the cancer risk, does the GI still want him to try Remicade and Imuran?