[Exim] Keeping aliases in a DBM hash...

I handle all incoming email with a single transport that loads up a "dbmnz*"
file from a particular subdirectory (depending on the domain). I've got it
working splendid, but with one catch... if I have just added a new domain
to the system, I have to define at least one alias or Exim will freeze
incoming mail complaining about inability to lookup aliases. I've tried
creating a blank file, but it says it cannot open the DB. If I define one
entry, it works out fine -- bounces addresses that are not defined, and
delivers to the entry I have defined. What I am wondering is how can I make
it so Exim knows that the DB is blank and refuses all incoming mail for that
domain?

--
Trevor Sky Garside
trevor@???