Custom PHP - Prevent vBulletin from timing users out?

[WorldCraft]

Hello, I run a PHP-based Ajax chatroom on my forum that uses existing vBulletin logins for the chat. By design when users logout of the forums, they are automatically logged out from the chat as well. Unfortunately the auto-logout will occur to vB's timeout option (AdminCP -> Cookie Options -> Session Timeout).

The issue here is that many of my users will just want to chat and not browse the forums. They will be constantly logged out because vB "thinks" that they aren't being active. Is there any sort of PHP function or plugin I can set on the chat script so that they will not be timed-out?

Thanks,
Mike