I've never used lemon-ade. I did use real lemons in a wheat beer a long time ago; looking for a summer thirst qiuncher. I went way over board on the lemons and it was sour. It mellowed out after a time and was drinkable, but man did the lemons come through.
Having said all that, I was watching a Leiny commercial last nght and they say they use lemon-ade in their Summer Shandy. I have no idea how much they use and I haven't tried their Shandy, but it appears to be a ommercially viable way to get lemon into beer.
Good luck. I, for one, would be interested to know how 1 gal into 4 gal works.