I feel kinda silly suggesting this... Or maybe I missed something... But wouldn't two rj-45 jacks on a motherboard work the same as two ethernet cards in the same machine... 
 
That is... To bridge two different networks...?
 
I mean, I have one machine with THREE boards in it... One configured to access my Admin net, and the other two to access two different division subnets...
 
Just a thought....
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