Reverse Magic Trackpad (turn 180°)
Solution 1:
sudo defaults write com.apple.MultitouchSupport ForceAutoOrientation YES did the trick for me on 10.9.5 (required a reboot). I haven't tried defaults write com.apple.trackpad.orientation TrackpadOrientationMode 1. Possibly the two methods are interacting strangely with each other?
Solution 2:
This appears not to work anymore on MacOS 10.12 (Sierra). Corroboration from Apple discussion forum, here: https://discussions.apple.com/message/30704137#message30704137