Well no need... Sunday mornings are a dream down town and the entire Greene Street parking garage is open and free, and just a few steps away from the registration and start/finish area. Here is a map of that area: http://cyclesdeoro.com/GranFondo_parking.htm
All the rider sign up activities will take place beside Cheesecakes by Alex, less than a block away from this garage. Piece of cake! :)