[exim] virtual mail redirect question

Hi. First let me say thank you for a nice MTA. I am starting to really
like the flexibility and power of Exim.

I have successfully configured it to have separate alias files for each
domain for virtual domains.  I am using 
    data = ${lookup{$local_part} nwildlsearch{/etc/exim/virtual/$domain}}
in the virtual redirect router so that I can have wild cards, giving me
the option, among other things, to have a catch all using a wild card
for a given domain.

In the domain alias file I have lines such as,

    joe         vince-joe
    leslie      vince-leslie

I have it configured where it will bounce with "Unknown user" if there
is not a .forward-<user> file in vince's home directory.

This causes me to go through two steps to add a new virtual user.
Add 
    user    vince-user
to the domain alias file, and add a
    .forward-user 
file to my home directory.

<my question>

What I would like to do, if possible, is only have to add the
.forward-user file.

Is there a way to configure exim so I can have something like
    *   vince-$local_part
in the alias file for the virtual domain, so that it will work like
a catch all, but forward to a unique local_part_suffix for each user?

It does not seem to expand variables, such as $local_part, in the alias
file.

Or, perhaps there is another aproach?

I am running exim-4.50