Well if he knows he is lactose intolerant and he knows he is getting symptoms from it, it is up to him whether he wants to eat the lactose and get the symptom of gas.
Is he having other issues along with the odor problem? Or is this something that started before the gallbladder removal? In some cases, changes in bacterial count or type could cause an issue, and if that's what's happening the use of some probiotics might be helpful. Lactose could be an issue, and if he used lactose-free products it would be helpful. But if he has problems with diary that continue with the use of something like lactaid, it could be more than just a lactose issue. Some people have problems with the major protein in diary - casein - a true food 'intolerance' or allergy and have to avoid all dairy.
Is he having diarrhea, too. That can happen after gallbladder removal and it can be the result of unregulated release of bile. When that happens, many individuals experience diarrhea, or much softer stools and urgency, and the fecal material could be 'odiferous' due to something life fat malabsorption.
You could try probiotics or lactose-free products or the use of products that will help to digest the lactose when he ingests it if the problem is simple and straight-forward, but if it's more than just odor, he really should try to sort through it with his doc's help.
Yes- he had his gall bladder removed like 2 years ago. Other than the fact that I KNOW he has a lactose intolerance and will NOT address it, this nastiness has been going on heavy-duty since his gall bladder removal. Basically, I am just trying to find an OTC remedy for the smell. Even it helps a little. Because getting HIM to seek help is like asking for a miracle.
Welcome to the gastroenterology community! Has he had his gall bladder removed? How long has this been going on for? Has he seen a doctor about this? It could be bacteria or lactose intolerance.