[Exim] multiple alias files and receiver_verify

We have a rather unusual situation where we have multiple (different)
alias files, and in some cases, an alias in one file is a wildcard
domain alias which points at a second (aliased) local domain.

i.e.

*@foo.com gets aliased to ${local_part}@???

user@??? gets aliased to user@mailstore

Yes, its gross and ugly, but thats the way our provisioning people
give me the data. It works great when the alias for user@???
exists, but when it doesn't, the mail still gets accepted, and then a
bounce message is generated saying `user unknown'. It seems that the
receiver_verify option doesn't recurse until it gets a definitive
answer (this could be problematic, I know, but its obvious other code
inside exim does it just fine).

Is there any tweak to exim 2.12 to allow the mail for an unknown
user@??? to be rejected during the smtp transaction?

TIA,

Gary