I wonder whether any parking buildings provide online reservation systems. You'd go online, print a reservation slip, then rock up and scan it to be let in. They'd have to be prepaid and have an expiry time, though, or else be for a specific vehicle. Otherwise you'd get scalpers standing at the gates overcharging for their acquisitions.
Mokalus of Borg
PS - In general, it seems like a system that would work.
PPS - Maybe not in every case, but it would function.