You can get a retrofit kit either from the VW dealer or from ebay, they are generally genuine but give it a sanity check, usually go for around £200 and its simple the fit.
Basically you remove the rear cup holder which is a seperate trim piece to the center tunnel, and bolt the armrest in its place, all holes are existing. The only thing to consider is there are a few varieties of interior, one is a largish cubby hole, and an alternative to accept a 6Cd changer or ipod prep, so make sure you get the most suitable for your needs.