The other option is to add a reversing camera, not quite the same but will cost you about £250 to do it yourself and what I'm led to believe is about 4-6 hours of work.
I've got all of the kit here, but haven't yet managed to find the 4-6 hours!
I can’t keep up with Audi’s names for all of the packs...and as others have said the “full packs” can be quite involved for the advanced.
However, if your car already had the 4x front and 4x rear parking sensors, it’s actually quite easy to add the auto parking stuff (coding and four parking additional sensors, that go on the bumpers looking sideways, rather than front or back).
Also as Generation Gav says, adding a camera isn’t the end of the world either.
Adding auto park and a camera would make a big difference in my opinion, even if it’s not the full “Parking assistant advanced” package with Pre Sense Rear, Side Assist and all that other nice stuff that actually just warnings of other traffic for the most part.