I have set this up before using 3-port firewall DMZ using single VCS-E LAN interface.
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i placed the VCS Expressway in the DMZ, Nat'd the Outside IP to the DMZ IP.
I only used the single NIC on the Dual Nic option.
On LAN 2 setup the DMZ IPv4 address as DMZ IP. Set the IPv4 static NAT mode to ON and then giving it the Nat'd outside ip in the IPv4 static NAT address field.
You will need to also NAT the Outside IP of expressway to the inside so that VCS control can hit the VCS Expressway by the Public Nat'd Address. You may also have to put a route in to point to the firewall in order to get to the Nat'd outisde ip of expressway from the inside.
There are several ways to do this but this has worked for me on several installs.
Cisco TelePresence Video Communication Server Basic Configuration (Control with Expressway)
Deployment Guide Cisco VCS X7.2
http://www.cisco.com/en/US/products/ps11337/products_installation_and_configuration_guides_list.html
I have set this up on 3-port firewall DMZ using single VCS-E LAN interface appendix 4 page 64.
Appendix 4 covers the various firewall scenarios.
Hope this helps.