redirecting to different networks

[Gustavo A. Baratto]

We have two firewalls (FW1 and FW2) in different locations, just connected 
to each other through the internet... We are running a DNS server (DNS1) 
inside just FW1. And later on a DNS2 will be inside FW2.
FW2 is ready, and the IP for DNS2 is already assigned... So, while DNS2 
server is not ready, is it possible to setup FW2, so DNS queries from the 
external world can be redirected to DNS1?

It would be basically an rdr reflection on the external interface, but the 
manual is clear this can't be accomplished... Is there any other way though?

Thanks for any input.

Cheers