B6 Rear Speakers - How Difficult?

[caledonia2k]

The kids are doing my head in. I need to scope this out for the sake of my sanity.
2009 B6 Passat Estate (S spec.. see poverty spec) with the RCD 500 (with the 'mix' button, not 'load') front door and dash speakers only.

I'd like to put speakers in the rear doors, so the kids don't ask for music to be turned up, then try to hold a conversations.
I've been told that if I were to run the cables and plug them in the back the unit will auto-detect the rears are plugged in and give me menu options to balance them with the fronts. Is this correct?

I've also been told that the wiring does not exist (did in the USA cars) and would need to be run.
So my next question is, how much of the trim needs to be removed? and how difficult is it to do?

If so, I've found shallow mount speakers that claim to fit the standard door cards without needing new pods. There are grill blanks there at the moment, would these work or do I still need the adaptors?

When I bought the car the dealer wanted an astronomical amount to fit these, so I didn't bother. I'm going to have to hang on to this car for a while yet, so need to address this if it's feasible.

Any help/previous experiences then please chip in.
Cheers.