[Biturbos4] Installing backup sensors?

[Nicholas Mistry]

I know this isnt really S4 related, but it is Audi related.   Recently 
my father leased a 2005 A8L and it basically came with everything, 
except the backup sensors.   He loves the car but his only complaint is 
the lack of visibility while backing up.   

Does anyone know if its possible to install the OEM backup sensors?  Are 
there aftermarket ones that are worth it?

Any info is greatly apprecated!

thanks..
-N