As nervewracking as it sounds, I removed my rear side windows by CAREFULLY pushing on the entire window, especialy on one side, and(since my interior was already gone) used a screwdriver to pry the seal and the window out. I have no idea if this is the best way, but it worked for me.
I started from the bottom rear corner and used the glass' flexibility (minimal) for my benefit. Once you get it started just pull on the seal and glass at the same time and pray.
On the other hand, I have 2 spares that you are welcome to should you break one (or both).