[Exim] Mail auth to Remote Hosts

This is a multi-part message in MIME format.
--
[ Picked text/plain from multipart/alternative ]
I have an issue where I need to send data to different smart hosts for different addresses. The problem I have is with SBC.

The smarthost address is smtp.sbcglobal.yahoo.com. This is a CNAME that ends up resolving to an "A" record with the name smtp-sbc-v1.mail.vip.sac.yahoo.com. This may change.

When I try to select the proper auth in my client auth statement, I use $host as the key is a lsearch.
$host has smtp-sbc-v1.mail.vip.sc5.yahoo.com in it instead of smtp.sbcglobal.yahoo.com and my lookup fails to get the correct username and password.

Is there a way to force $host to the name of the host specified in my manualroute router instead of having it looked up and then reverse dns'ed to get the host name?

Bill
--