Installed my Bluetooth / Aux In / USB module. It's a CruxBTS-VW2 that plugs into the factory stereo where the CD changer would go.
I placed the module in the little cubby in the glovebox, next to the manual slot. I drilled a hole in the side there towards the back large enough for the plug to fit through, and after some juggling with a flexible retrieving tool, was able to pull the cable through into the stereo slot. From there it's just plug and play, and works nicely.
I just have a little fuzzy noise going on (sounds like a dusty record), but I only hear it with the engine off, once it's running, it drowns out the noise.
I guess that hooking up the ground will resolve this, I haven't found a good ground point back there yet that I can get to without removing trim, so that will come later.