Sendmail and multiple RT instances

I am trying to create a second RT-3.6.3 instance on an RHEL4 server.

The server is fully into production mode for the original instance (which
has been working fine for quite some time).

I have a separate installation for the second RT-3.6.3 instance and it
seems to be working fine in all respects, except one. I would like mail
from the second RT instance to appear to come from a different server name.
However, the Reply-To address is being overridden by the Masquerade from
Sendmail and therefore appears to come from the same server as the original

I had to configure Sendmail to Masquerade the envelope and the entire domain
as a fixed name in order to compensate for some poor legacy decisions.
However, this level of rigidity is now a problem for me.

Can someone here recommend another way to configure RT or Sendmail to achieve
my end goal?