Exchange Question - Send As

Hi
I was wondering if it is possible to change the send as setting in exchange so that when a user sends an email as another user, the mail will be stored in the second user's sent items, rather than (or as well as) the first user.

We current use a number of dummy mailboxes for projects, and multiple users have access to these mailboxes. For central administrative purposes, I have been asked to implement this. Currently users CC the project mailbox, but that is not considered acceptable, (don't know why, maybe to conserve server space.)

Important info: Exchange 2003 Enterprise Edition, Windows Server 2003 SBS edition.

Any suggestions?
Thanks,
chuck.