[exim] Exim in virtualhosting enviroment.

    I wish to set a exim in a virtual-hosting enviroment. First off, i 
had work witch Cpanel, so i understood who exim works, but i not a 
exim-master :-)
    Structure will be:
       - $HOME_ROOT/$user/$domain.com/conf/mail-filters       -> Has 
exim filters , who aply to all domain.
       - $HOME_ROOT/$user/$domain.com/mail/$virtual_user_name   -> 
maildir for email

    Data for exim will be:
       - /etc/exim/localdomains: list of localdomains in this server
       - /etc/exim/userdomains: list of domains, and user who own it. 
Example:
            test.com: testuser         -> domain test.com is owned by 
user testuser, and mail for this domain is in 
$HOME_ROOT/testuser/test.com/mail/virtual_user_name
    In exim.conf, i define $HOME_ROOT as a macro. $user and $domain.com 
may vary, depends on email from.

    I want to work witch exim perl support ( I really like perl :-) ), 
but i have some questions about this:
    1) In perl, can i use Exim::expand_string to get the value of 
HOME_ROOT ?
    2) someone has a similar configuration ? how is the best router and 
transport to work whitch ?
    3) i suppoused i need two different transport, one for filters and 
one for virtual_user_name. Isn't it ?