how do I enable multiple sshd ports in Mountain Lion
Welp, I found the answer after a few more days of research, with the help of a response to this MacWorld post  I thought there had to be some way to include multiple ports in the one .plist file, but I couldn't figure it out.  You can add an "Alternate Listener" key to ssh.plist for the extra port inside the Sockets scope, such as:

 &lt;key&gt;Sockets&lt;/key&gt;
 &lt;dict&gt;
         &lt;key&gt;Listeners&lt;/key&gt;
         &lt;dict&gt;
            (...)
         &lt;/dict&gt;
         &lt;key&gt;Alternate Listeners&lt;/key&gt;
         &lt;dict&gt;
            &lt;key&gt;SockServiceName&lt;/key&gt;
            &lt;string&gt;ssh-alt&lt;/string&gt;
         &lt;/dict&gt;
 &lt;/dict&gt;


Notice the ssh-alt string for SockServiceName.  The original "Listeners" key remains as is, so you have Listeners and Alternate Listeners.  You have two entries in /etc/services for ssh and ssh-alt like:

ssh              22/udp
ssh              22/tcp
ssh-alt        4790/udp
ssh-alt        4790/tcp


which preserves the port 22 internal access and creates access via port 4790 for external use (assuming you disable port 22 and port forward port 4790 on your firewall/router.