Did you ever think about changing his diet? I was dianosed with CD 2007 in the lower colon and I had two massive and painfull rectal fistulas that surfaced about an inch from my anos and tracked back to my lower colon.
GI insisted that I go on remicade as he said this is the ONLY way to heal fistulas as large as I had, and that nothing else will work. Well, like you, I was hesitant to turn off my immune system, so I did some research and I decided that before going with the hard core drugs, I would try a more natural approach first. I decided to try the SCD diet approach .
I dedicated myself to this diet and I followed it with fanatical 100% dedication and without any cheating. Well, after 3 months on the SCD diet, both my fistulas started to show signs of healing, and all the white mucus that I had in my BMs was gone. By 5 months, both fistulas had healed so much, the surgeon actually had to remove the setons so they would heal more. By 7 months on the diet, both fistulas were completely gone, completely healed, and I had no other symptoms from my CD. The only drug I was taking along with the diet was 1000mg pentassa 3 times a day.
That was in 2007 and I have not had a symptom or a problem from fistulas or a problem from my CD ever since. Thw surgeon said he had never ever in all his career working with crohn's patients, he has never seen fistulas as large as I had heal without remicade. He said just keep doing what ever you are doing because it is working for you.
I had a colonoscopy two years ago and there was no sign of any active CD in my colon. The only thing they found was some scar tissue where the fistulas had healed, but nothing more, no CD.
I suggest that you read the book "Breaking the Vicious Cycle" which goes in detail about how this doctor cured her daughter of UC with the SCD diet. This diet is not easy to follow because you have to give up a lot foods like all bread, grains, rice, potatos, corn, processed foods, all foods with sugar, all diary, etc. It also doesn't work over night and it takes time, but you have nothing to loose by tyring it, and all to gain if it works for your son.
There are many people on this site that have had great success just as I had, so there is a wealth of information to be had here. Read the book, and see what you think.