Starting with Version 3.0 Just In Engines (mac or linux) can be activated for Live Cut. Just In Engine activation keys have to be requested for this to work. Refer to the chapter Activation to learn how to request and enter an activation key. If the Just In engine (either Just In Mac or Linux) is not activated for Live Cut, just:control can not switch into Live Cut mode.
The Activation Tab can be found within the just:control Configuration Panel.