catchall non-existent user address

[Vernon A. Fort]

I'm trying to find a way to configure a local cyrus catchall account 
with the relay_recipients_maps.  Basically, i'm moving 2k+ users from 
the aliases file to using the relay_recipients_maps build from an ldap 
query from exchange.  All i need is a way to catch all non-existent 
users (temporally) until I'm satisfied we completed the conversion 
correctly.

I've googled, read and testing for hours but cannot find anything to 
make this work.  Any advice?

Vernon