We found Finnegans was the best place last year to drink up some "liquid courage" before heading out. It was convenient too since we were pretty close to the soundstages. We managed to hit four houses before the crowds caught up.
Also, once you get into the park keep an eye out for the girls selling "Jello Shots"---Literally, they are huge syringes filled with jello and alcohol. Our group had numerous "injections" over the course of the night!