Help setting up NVG510 in bridge mode to Airport Express router

Recently had to switch to U-Verse which forced me to use the Motorola NVG510, which is all fine and dandy. My only issue with that is I no longer have a guest wifi network for my daughters "friends" and do NOT like having them on the same network as every device in the house (printers, TVs, etc), so I am compelled to figure out how to get this NVG510 into bridge mode so I can get my Airport Express router back up and running so that I can get my guest Wifi back up and running and sleep better at night.

I've searched Google extensively and tried many, many different approaches and all of them failed with Double NAT errors aplenty.

Is the idea of doing this even possible? And if not, is there another device I can purchase from AT&T or anywhere else for that matter that I can use to replace the NVG510 that will make this goal possible? Either I'm getting a guest mode up and running so that my daughters friends can use wifi in my home or I guess U-Verse will have to go (which will be unfortunate as it seems to work rather well and would have to have to switch back to our local cable providers broadband offering all because of a poor choice of gateway offerings).

Any help anyone can provide would be extremely appreciated.

Thank you!!!!