Haven't seen anything on rear AC retrofit, just Rear USB jack retrofit. I've got the erwin guides for the Golf/GTI/R so I'll see if I can find you a diagram on the ducting and such.
As to your smog comment, we have 8 year smog abatement on new cars. so 8 years from date of purchase is first smog for cars newer than 2010 I think.
Edit: Not finding much. I find the front console removal that mentions the duct, but the shifter removal doesn't mention the ducting that runs to the armrest at all. I'll see what the dash removal says on ducting.