the answer i was looking for is:
updating the tcp_local section in imta.cnf file with the keywords:
daemon <fully qualified domain server name of the gateway>
then saving the file , making a backup copy of the config_data file, recompiling this file using:
imsimta cnbuild
Restart messaging server services
I'll give you a brief description here but you really should look at the documentation on the re-write rules for a more thourogh discussion.
But, instead of a routing table in iMS you use the re-write rules to manipulate how mail goes through the system and out of it.
For each domain you want to force a route on you would create a rewrite rule pattern to match that domain and in the template that follows the pattern include the host name or channel name you want to mail to be delivered to.
-Chris