I have a test script you can use..
Add a playlist that plays a single image, and schedule that playlist first. You'll need to do this with an interactive playlist.
Open the image in the playlist, and go to advanced, then add command. You can use this with either Send UDP or Send Serial CR.
Choose Send UDP if your unit has ethernet plugged in, or Send serial cr if your unit has a serial port.
For the parameter, add to kill sync on the display:
or to wakeup
This should work over vga or hdmi, but another user reported his displays didn't respond to the command.