Port Forward Static Public Ip to Private Static IP in a Uverse 2Wire 3801HGV

With those uverse modems the best way to accomplish this is to put the modem in 'bridge mode' and then have your own router sit behind it that can do 1 to 1 NAT of your public IP to your private IP.

I was wanting to do that like I've done on the traditional AT&T DSL business accounts but AT&T says this Uverse unit cannot be bridged.  I don't know it if is a technical reason or some AT&T policy reason.  AT&T won't give me a specific reason why it can't be bridged, they just told me it can't.  

There is a port forwarding feature in the unit to port forward to a private ip address but when executed, it does not use any of the assigned static public ip addresses, instead it uses a dynamic public ip address completely different from the range of assigned static public ip's .

From within its firewall I found a place where you can port forward one of the assigned static public ip addresses to another one of the assigned static public ip addresses but it won't allow you to select an existing static private ip address.