SMTP Mail Routing - Relay Host Question

I have an application that will allow users to send a mail message to a pager gateway. The pager gateway is not a Domino server. It listens over SMTP on the network for incoming mail requests and generates an outgoing fax based on the incoming email message. All the users of the application have a home mail server with a relay host entry that routes mail to a server in our DMZ that filters the mail and sends it on. This, of course, is not the pager gateway. My question is this, is there a way to bypass the relay host for a specific domain address for the pager gateway or do I have to not use a relay host entry and set everything up to route using Foreign Domain entries? Any help is appreciated!