Recently, I used Adam's write up HERE to add the auto down function to the front passenger window.
This got me thinking about adding auto down rear windows as well, so I took apart a spare master window switch I had laying around to see what wires would need to be tapped to make this work.
I removed the back cover of the master switch after cutting all the wires and this is what you get
Now, with Adam's write up for the passenger side window you tap into the BLACK, BLUE, and WHITE wires. Given that the BLACK and BLUE wires are identical for all the windows, the one that controls the passenger side would be the WHITE wire.
Using this same thought process, I am led to believe that to add the auto down feature to the rear windows you would need to tap into the GREEN/YELLOW wire for the passenger rear side and the RED/BLACK wire for the driver's rear window.
So, given this information I am confident that adding the auto down relay to the rear windows is essentially the same process as the passenger front window except for the different wire colors.
I will add more pictures once I start the process of adding the relays in and will report back with video
EDIT: mods, can you change the title to "Auto Down Windows, Additional Thoughts"? Didn't catch the backslash for some reason