Changes pane: how can I make double-click Show Diff?

In the Changes/Local pane, double-clicking a file opens it in the editor.  I'd like to make it do Show Diff instead.  Is that possible?

I tried going to Settings | Keymap to do it.  There are two commands "Show Diff" in the "Other" section, with nothing to distinguish them.  I tried adding a mouse shortcut -- double click -- but it didn't work.  All that accomplished was to make double-click do nothing at all in the Changes pane.