That did not work. But a two finger tap on the trackpad, which is supposed to be eqivalent to control-click, does work! I've been trying to sort this out for ages. Now I've got it!
You can click 'Forward' on the navigator buttons, it cancels any pre-moves. (Any of the navigation buttons, Beginning, back, forward, or ending, cancel pre-moves, but 'forward' or 'ending' are quicker!)
How do I do this on a Mac? There is no right click. Tapping on piece does not work.