I was only thinking of westfalia when it came to towbars. They still list the 4x4 as under development.
westfalia towbars
I never considered thule. I have a feeling that they are actually made by Brink
They do list both fixed swan neck and detachable towbars for the 2012 on panda 4x4. You have to go through the wizard
http://www.thuletowbars.com/
They detachable tow ball looks the same as I have on my VW (brink towbar) I am glad to see that the wiring kit from thule does not require routing to the battery, but dismayed to see that you have to cut some wires to the rear lamps.
The westfalia doesn't need cutting of the rear wires but you need need to remove the scuttle panel (I think that's what it's called) below the front wipers to run a wires to the battery.
Neither option is ideal, a hybrid of the 2 would be great though.
Still, if you're letting the dealer fit, it won't matter.
Good to see that you can at last get a towbar.