You could use it as a post-workout shake... When I used a weight gainer, my preferred method was to take it before bedtime but ONLY if I didn't hit my calorie goals that day. Personally, I hate weight gainers, I think they taste way too sweet on average.
A cheap alternative is to just add some olive oil to your whey shakes, that is if you don't mind the extra fats. Olive oil is very calorie dense and when you put it in whey, it doesn't effect the taste much at all.