DMZ GUP Live Update Configuration

I am trying to configure a GUP in our DMZ so that clients over the internet can "home" back to the SEP12 Enviroment. We have placed a Server in the DMZ configured the firewall ports, internet DNS etc. The last step I am missing is where do i define this in the live update GUP polices to tell clients if you are not on the LAN go to this GUP.  I can add a explicit GUP but it required a LAN subnet.

Any ideas would be appericated.

Thanks