exim and sendmail-like virtusertable

["Peter Lieven" <lieven@inity.de>]

i want to set up exim with virtualhosts and virtual passwd and alias
files.
so far anything works perfectly with a patched gnu-pop3d version.
but i'm missing a solution for the special token in sendmails
virtusertable which
allows all unassigned email-adresses to be sent to another domain
(e.g.: *@domain1 -> %1@domain2)
i want to be able to create aliases for domains and virtual mailboxes
(no problem 
so far), but i want all unassigned emails of a virtual domain to be sent
to another domain.
i know that it is possible to send all unassigned emails to a specified
email (e.g. postmaster) by using a * in the alias file, but i found no
solution
to create a rewriting rule like it is possible in sendmails
virtusertable.
i can add a general rewriting rule (e.g. *@domain1 $1@domain2) in the
exim.conf,
but this overrides all virtual users and aliases.

any ideas?

thanks,
peter