Video from 2014 showing how to fit an armrest you may have purchased from a breakers yard or online.
I didn't record this but I did drill a hole on the inside of the arm rest and fit a USB extension from my head unit, the wire was hidden inside the trim and worked nicely, so that is possible if you are wondering.
Since then Bluetooth in cars has taken off so its unlikely you'll be wanting to do this.
I have lost the footage at the end showing the plastic trim being fitted, I'm surprised the videos have lasted on my hard disc this long, I have moved 3 times since recording the fitment, and changed cars 5 times.
I think this was my favourite car, at times I wish I had not sold it, fixed all the rust, replaced the entire interior with black trim and GTI bucket seats, the vents with Bora illuminated ones, the map light with the Passat w8 one.