Removing calendar from Exchange 2007

Greetings,

I have a client who has two organizations using one Exchange 2007 server (SBS 2008); all employees are part of both orgs. Each user has two mailboxes: user@orgA.org and user@orgB.org. They like keeping two distinct sets of mail folders, but want to use just one calendar: orgA. The problem is that sometimes people look at the free-busy of user@orgB.org. I know that one way around this is to change the display names to something like "Name (ORG A)" and "Name (ORG B)" so that when someone wants to check another user's free-busy, and he/she starts typing in that user's name, they will see both orgA and orgB names and can select orgA. However, I'm wondering if it is possible to remove the calendar from an Exchange account (the calendar that is automatically created with an Exchange account), so as to avoid confusion?

Thanks,
Andrew