I suggest that you help him build up his digestive flora. The way to do that is to use probiotics. I would use kefir grains raised with milk and then pour a little kefir on food for each of his meals.

There are places and forums online for use of kefir where you can get kefir grains for free, just for the asking. They are very easy to keep going and will make probiotic rich food forever with regular care. (the stuff you get in stores does not contain kefir grain).

We love to use kefir in fruit smoothies. Just pour a cupful into a blender, add a frozen (destoned) peach or strawberries and half a frozen overripe banana and you get a smoothie that which is free of refined sugars, is good for the humans. Helps symptoms of IBS and IBD in humans and animals alike.

A little information on probiotic benefits (for humans) is here at this link. (read the "Power of Microbes" which applies pretty much to all living beings. Due to the types of prepared food we eat and the chemicals we take in, often our 'natural balance' of natural digestive flora is off kilter. So you might give this a shot. The types of bacteria on kibbled food are different than what should be in normal flora.

Commercial yogurt or probiotic pills btw are not even close to the same thing.

Will it cure the gas? It could help. The gas forms because the wrong bacteria are involved with breaking down the nutrient in his gut. When his gut normalizes, the 'good' bacteria will help him become more efficient. Just read the link above about probiotics and it will help with understanding what is going on.