I fitted an armrest to my 07 GTi.
Got it from Ebay - a breakers I think. Cost me £80 delivered.
It was missing 2 bits - the handbrake slide cover and the cd changer!
Cover bought from VW for £11, IPOD dock to fill cd changer hole supplied very kindly by Very Cherry for free!
Fitted the whole lot myself in about 30 mins - its really straight forward and simple.
Didnt bother with the ducting - looked to be a pig of a job! There isnt often anyone in the back of the car so it wasnt worth the hassle!
Andy