I have F670L from airtel with locked down user. All I did for that one was F12, inspect element and literally modify HTML code line which has "disabled" attribute tag on the option for bridge. Then create new WAN profile, you cannot choose Bridge via GUI, again using HTML, set the option tag's value to "bridge" and its done.
Here is an image of what I did. As you see in the right side, after creating a new profile, set the VALUE TAG TO BE "bridge". The title/text tag doesn't matter as its just for visuals.
See if this works for you in Netplus. IF it does, win win