[Exim] vacation and checking against the .db

I've tried the vacation delivery in a .forward filter file, and that
works fine.

However, I need to be able to detect whether a sender of the message is
already in the vacation DB (meaning he won't get an autoreply).
In such cases, I want to forward the message to another address.
Is there a way of detecting whether an autoreply is sent or not?

I've been toying with using the external vacation program, together with
its -l option to list the contents of the DB, and then checking the
output of that against the current sender, but I expect that doing it
inside Exim will be a much cleaner method.

Still using exim 3 on that particular system, although that system is
next on the list to convert to 4 (I've done most already :-)


Thanks,
Paul Slootman