Drat! Raven got there 1st (whilst I was away checking that things hadn't changed in P6, and setting up some images to show the way that displacement works..)

However, 'cos I'm egotistic and hate to waste time, I'll post what I saved anyway...:-))

The above is a very simple set-up, seen in the pose room. Just a (green) cube and a one-sided square, offset very slightly from the cube.