I did an Archive and install update to 10.2, and it preserved my Finder prefs, including the Trashcan in the Toolbar. I've still got a 10.1.5 partition on one of my drives, and the one time I dragged the trashcan out of the Toolbar, I couldn't get it back by teh 10.1 trick, so I copied the 10.1 prefs file to my 10.2 partition, and voila!
CV