How to add more than one password for protecting posts and pages?

Hi all,

The WP Codex states that only one password is stored when you password protect a post or page. I'm looking for a plug-in or hack which allows me to store more than one password.

"What are you doing this for?"
I want to allow certain paid users to view data results on a protected page, but if they stop their recurring payment I will delete their password. There will never be more than 30 users who need to access this page. I'm trying to keep this independent of the Membership plug-in since I will be running that as well and don't create another member type for this purpose.

All suggestions welcome. Thanks!