It he's not into this stuff, he's going to think you are nuts. But I will tell you, this really works. And it's very easy to do. Get some Sunflower or untoasted Sesame Oil. Have him put a tablespoon in his mouth and swish it around for 20 minutes, every morning before he eats anything. Gargle with warm salt water after. Tell him that the other result will be white teeth!
I bring up a ton of mucus after I do this. People's sinuses reported draining immediately, and stay clear for the rest of the day. It's a very odd therapy, but it works amazingly well. Easy and inexpensive...give it a try.