[exim] copying all email to an address in a virtual domain

        I have virtual domains set up with exim4.  I would like to
        copy all email to a particular address to another address also,
        as one would usually do with a .forward file.  However, since
        the address is on a virtual domain there is no home directory
        in which to put a .forward file.

        I am not forwarding the email to a real address, rather I am
        trying to make all email to one address also be piped to a
        command that delivers it to RT.

        I do have aliases files for each virtual domain.  Is there a
        way to do this with aliases files ?  If the address is
        a@??? and I want email also copied to b@???, should I
        be able to do 

        a: a@???, |/opt/rt3/bin/rt-mailgate

        without causing a loop ?  I tried this and it didn't loop but
        also didn't seem to copy the email.

        Is there some bit of code I can put in exim4.conf to do this ?

        Here is how my virtual domains are set up:

        The non-virtual and virtual domains are listed in "domainlist
        local_domains".  The local parts are listed in
        /etc/exim4/domains/$domain and the aliases file is
        /etc/exim4/aliases-$domain.  The mail goes to
        /var/spool/mail/domain/localpart.

        Should I be able to just copy the "userforward:" stanza that
        is already there and name it "virtuserforward:" and change the
        $home/.forward to /etc/exim3/$domain/forward-$local_part ?
        When I tried this it first complained when I left out
        check_local_user, and it didn't do anything when I left it in.

        Any suggestions will be appreciated, including just links for
        where else to look.  I have searched the archives and the
        wiki.