[Exim] Virtual Names & More Complex

Hi, I'm looking at Exim as our MTA replacment for good ol'sendmail. One
thing we are trying to figure out how to do is create mail accounts
without having to create 'user' accounts. We have a web hosting model
that does not require the user to need access or ftp to a machine, its all
browser based, however we would like to provide email to some of these
clients without having to maintain more user accounts. I know Exim can
tie a domain to an account, but this still needs the account.

Does anyone know if Exim can solve this delimma, or point me to a place
that can?

-R