What you could get him to do is try and count the calories he eats for a few days. To lose 1 pound, he would need to cut back 3500 calories.
i.e. Suppose he maintains his current weight with 2500 calories per day. Eating any amount lower than 2500 will result in a weight loss.
So for example, eating 2400 calories, which is 100 calories less would result in a 1/35 lb loss per day or a loss of 1lb every 35 days - roughly a month. At this rate, he could lose the weight you want him to lose in roughly a year. I wouldn't recommend cutting down too fast because it will obviously make him painfully hungry. Cutting 200-300 calories will very quickly put him to the weight you desire. Just remember that calories work both ways and that if he were to cut 200 calories per day 6 days a week = 1200 calories, and then go out and binge 1 day a week, he likely won't lose weight very quickly. I personally trimmed 25 pounds off this year as a New Year's Resolution - I found the easiest way to do it was to add up the calories after each meal. That way, if I went out for lunch to a fast food restaurant, I could make adequate compensations later in the day - like eating salad for supper. You can get pretty much any fast food restaurant calories online by googling them up. Most foods can have their calories found also by googling up (if they aren't listed on the package). Wishing you both the best on this noble cause