changing from address for UUCP mail?

[Doug Hughes <doug@happy.vf.ge.com>]

We have a sun here that does UUCP to one other host.. the rest
of the world does not have knowledge (in the mail SMTP sense)
of the existence of this gateway.  Thus, if someone were to mail
to host!user from anywhere but this one gateway machine running
zmailer, it would get rejected. It's a temporary setup until
they get IP.  It's no problem mailing to host!user@happy.vf.ge.com.
  Here's the question.  What do I change so that when I go to reply
to a message from host!user, I get host!user@happy.vf.ge.com.  I
thought the relevant configuration might be in crossbar.cf. But,
I'm not sure exactly what I should put in there to tack on that 
additional @happy.vf.ge.com so that reply-to will work correctly
when mail goes to a site other than happy that doesn't know about
this UUCP connection.
  Any suggestions?
 Doug Hughes				GE Aerospace
 doug@happy.vf.ge.com			doug@doc.vf.ge.com