DisplayLink Mac OS X Software - User Guide
Using both extended and mirrored displays
To work with both extended and mirrored displays, turn o mirroring then in the Arrangement pane press and hold 'cmd' and 'alt' and drag and drop the display you wish to mirror over the primary display.
Repeat this with each display you wish to mirror, those untouched will remain extending.
Changing the main display
You can change which is the main display by moving the Menu Bar between displays. Changing the main display aects where new windows appear and the position of the Dock.
The ‘Menu Bar’ can be moved so that it is shown on an alternative display. Clicking the white menu bar and dragging it to the desired display will perform this action.
Display Preferences:
Moving Menu Bar
Page 9