You want that all shown controls at the UI should use the gamepad controls but as no UI is shown (HUD level), as you fight etc., it should look like keyboard?
Not sure if this is possible. One would have to exchange a lot and hack into many functions so that the gamepad stuff is not shown again after each update, like health lost -> gamepad healthbar changes -> needs to be replaced at tll possible locations against keyboard updates.
etc.
All addons that I know did it the other way around. e.g. AdvancedDisableControllerUI which shows the Gamepad UI at the HUD and in inventories and menus it keeps the keyboard menus. It's not working anymore for all cases but at the comments someone wrote you need to open and lsoe the inventory 3x times after login to make it work properly.
I doubt that there is an easy way to create an addon for your use-case as it is a very special addon use-case, and it's not that simple to "exchange" GP against KB+M stuff. Very time consuming to find and test all related controls, scenes and fragments+ keep them updated as you move/fight/gain XP etc.