Why does it need a software update? I had the same HU in my first FL Leon FR and as standard comes with 4 channel amp and 4 outputs, unless SEAT have turned off the rear speaker option or changed the firmware since the Leon switched to the RCD310 for MY11?
Doubt VAGCOM will do it it will be the actual stereo firmware and possibly Canbus update, but would be a very strange thing to do indeed. As when the speakers were removed from the spec as far as I know the HU or firmware did not change, unless anyone can tell me different???? Worth trying to connect a some speakers up to the rear output and seeing what happens? Bit like sticking an MDi cable in the back of the HU and seeing if it enables the USB/iPod option without a firmware update.