Paid, Unseated, and Keeping an inventory

Hello all,

I'm trying to setup an event that we want to basically sell reservations.  That is, we want to collect payment, but not seat them because our client wants to manually seat them.  I've figured that out by creating a new MOS that allows us to take payments without seating/ticketing, but how do I keep an inventory of these sales?

What worries me is collecting money on these orders and over selling the house.  I feel like I'm missing a step.  Any ideas?

Thanks!

AJG