There are battery feeds, several of them, to the central locking pump (all cars), which is in the passenger wheel well (convertibles) or under the floor mat (coupes).
There are also two battery feeds to the power top module (convertibles) in the driver's side rear wheel well.

I know of no ignition switched power in the back of the car.

I've never owned a coupe. Getting to these battery feeds is SIMPLE in a convertible (you just raise the lid and the wiring harnesses are exposed), but I have no idea how to remove the trim of a coupe.
If you want to play around with this, you should download the service manual from our tech area. If you really want ignition switch power (WHY?) it is a simple matter (again, in convertibles) to run a line to the back from the underhood fuse box on the driver's side.