adding virtual webmail users, freebsd6

[Dave]

Hello,
    I'm setting up a webmail solution on freebsd6. So far i've got the 
underlying MTA Postfix working. I've installed Squirrelmail from ports so 
far all of this installed fine. Now i want to give another user an 
administrative function, adding virtual users, so that i won't have to 
manually add real users whenever a new account is needed. Is this doable?
Thanks.
Dave.