We just ran into this back in April. We actually explained to the people at the ticket counter that we were staying 4 days, and that the Saturday of our trip was a blockout day on the Deluxe AP which we wanted to buy. We were going to buy parkhoppers and upgrade on the last day, but they didn't even require us to do that, they printed us out a blockout ticket for the Saturday and let us buy the APs then and there (probably to get us hooked up for the higher amount up front

)