When I went a couple of years ago they held the "party" in the clubs in the stadium, and they had a line on the field to get up the tunnel and into the locker room. They basically walk you in the in-door, down a ways, and out the out-door. All the uniforms are out on display in the lockers. They had Marv Levy's desk brought down as a kind of museum display. And you could also look into the weight room.
Now they have the "party" in the field house. I'm not sure if they have the game-day games set up for the field goal kick, fair catch etc or not.
Call your ticket rep for more info and to see if there are still tickets available.