All you need to do is create a display profile that displays the layers on the third monitor. In the settings under "Display Settings" select the create new profile button. This will open the profile editor (icon of a sheet of paper). On each layer find "Size and Position" and change the monitor to "Monitor3".
Now close the dialog and ensure the new profile you have created is selected. You should now see your layers appear on the third monitor.
You can have different layers displaying on different monitors if you wish.