[Choronzon]

If he wont listen to you effectively nothing. I know this is not the answer you want to hear but you can only help people who help themselves. He sounds like he is in nowhere near the shape required for any kind of sport but an hour or two walking a day would be excellent workout. If the diet is failing then quality of food is probably an issue,high quality vegetables and meat/fish cooked simply (no sauces ),no vegetable oils,minimal milk and bread products.The more boring and tasteless the better.

You can consider a low carb diet as well(provided its clean),humans are normally perfectly adapted to eat carbohydrates but he might find it easier if he has problems with insulin regulation. And he should stop working already,time for health related retirement.