It'll work fine. I've done it with beer and hard lemonade. In fact, I have 2.5 gallons of hard lemonade in my kegerator in a 5 gallon keg right now. I didn't want to use my precious 3 gallon ones for my daughter's hard lemonade, so it's in a 5 gallon keg. She's not even drinking it, though- her husband is, but that's really beside the point I guess!