[exim] Last Config Issue

We have a virtual user file which looks like

someone@???:    popbox1
*@domain1.com:              catchallpopbox1

someone@???:    popbox2
*@domain2.com:              catchallpopbox2

Config (ROUTERS) has:
#POP# Virtual Address
virtual_aliases:
         driver          = redirect
         allow_fail
         allow_defer
         data =
${lookup{$local_part@$domain}lsearch{/usr/exim/pop3.aliases}}
         file_transport  = address_file
         pipe_transport  = address_pipe
         debug_print     = "R: virtual_aliases for $local_part@$domain"

I want this to be conditional on finding the user, but otherwise to find the
catchall with the *@

I tried
#POP# Virtual Address * catchall
#virtual_aliases_catchall:
#         driver          = redirect
#         allow_fail
#         allow_defer
#         data = ${lookup{*@$domain}lsearch{/usr/exim/pop3.aliases}}
#         file_transport  = address_file
#         pipe_transport  = address_pipe
#         debug_print     = "R: virtual_aliases for *@$domain"

BUT both get activated and I need conditional on the first and catchall on
the second if an exact match is not found.

Thanks
Gary