Can you do some research to show how him what he's eating - particularly snacking on - is making him feel hungry all the time.
Have a look at leptin, insulin and ghrelin and see how a high carb diet gives 'sugar spikes' which in turn makes you hungry. People just do not realise how much of ordinary food the body will treat as sugar.
the Wheatbelly blog has a lot of info about this and explains it much better than I can.
I'll use 'turn to sugar' in this list, it's a lot more complicated than that, but it gets the idea across about the type of foods you eat and shows the effect they have on your body. I used to eat food similar to this.
e.g. breakfast weetabix and jam on toast. The cereal and bread will also turn to sugar as well as the jam. There's nothing here to prevent hunger after an initial sugar high mistaken for satiety as a full tum. Soon hunger pangs start.
snack biscuits = wheatflour turns to sugar, there's also fat and likely not a good one e.g. palm oil, again no protein. Up goes the spike and soon there's a crash, hungry again.
lunch sandwiches and crisps. the bread and crisps turn to sugar. you're beginning to see the pattern now, up and then down...
snack cake = wheatflour which turns to sugar plus more sugar. way up and quite quickly down again and starving hungry.
main meal potatoes/rice/pasta with meat or fish in a sauce, dessert. Carbs turn to sugar as do most desserts stuffed full so huge sugar rush followed by a steep plummet.
snack chocolate = there you go, sugar and fat. high again, then it depends if he can go to bed before yet more hunger pangs start, or if he decides to try something for supper before bed.
Do you see how all day he'll be yo-yo ing from initial sugar highs to sharp crashes, rinse and repeat all day. Basically it doesn't matter how many times he tries to feel full eating that type of thing, it won't work for long. About an hour to an hour and a half later, he'll be ravenous.
If he changes to a much more low carb, adequate protein and high fat diet he won't feel hungry because he'll no longer be creating those yoyo sugar spikes.
Have a look at the aforementioned Wheatbelly blog for recipes and Michael Mosely's latest one thebloodsugardiet.com/