12 year old boy with IBS

My 12 year old son has been diagnosed with IBS. He has had it for a number of years but it is particularly bad this year. He seems to be a text book case according to the GI specialists we have seen.The attacks now hit him about 3 to 4 times a week, often ( but not always)after a hockey game or any other strenuous exercise.He is normally a healthy, happy boy but this is taking over his life. The research seems to point to stress in many cases but he doesn't appear to fall into that category. Nor can I isolate any particular foods, except very fatty foods which he no longer eats.We have added fibre to his diet.As we have seen a number of specialists, all of whom confirm there is nothing we can do, we are at our wits end as it is devastating to watch our son go through these attacks so frequently. At some stage it will affect his schooling, although he is currently up to date.Does anyone have any suggestions?