[Exim] how to trash unrouteable domains before expiration

On occasion, I get email to an unknown address at my domain, and that email
is returned with an appropriate message.

Sometimes this bounce message cannot be delivered, and I would like to get
them off the queue prior to expiration.

The following seems to handle most of these cases.

trash:
driver = appendfile
user = exim
group = exim
file = /dev/null

misspell_expire_undeliverable:
  driver = lookuphost
  condition = ${if and {{> {$message_age}{43200}} \
               {match {lc:$h_subject:}{address not found}} \
               {match {lc:$h_from:}{misspell@???}}} {yes}{no}}
  transport = trash

My problem is that some of the bounced messages are going back to
non-routeable domains (like a typo's on a domain name), and since the
router cannot route the message, it never gets passed to the transport for
delivery.

Does anybody have any suggestions on how else to handle these bad addresses ?

Thanks in advance.

mark