Well, there's an epic thread on this very topic that's been floating near the top of the first page for the past couple weeks. Anybody who gives you a bulking diet with a specific calorie total is a complete moron; what moves the scale for one guy won't be enough for another. So just make sure he's eating frequently, getting protein with each meal, and adjust the quantities until he's gaining weight at the rate he wants. It should be obvious, but over time he'll have to increase the calories to account for the higher caloric expenditure that comes with more muscle.
IMO, those weight gainers are a joke both in terms of price and health. If you're going to get a couple thousand calories a day from shakes, there are better ways to do it than high-GI carbs disguised as complex carbs (i.e., the maltodextrin that's used in a lot of weight gainers). Use milk to get those extra calories or make your own shakes with protein powder, oats, and peanut butter/nuts/oil.
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