You could use FXRobot to fire a KeyEvent on a timer - just get it to send F16 key press every 10 minutes or so.
F16 shouldn't be used by anything, but will register as a key press and stop the screen going to sleep.
You can use the jAWTRobot library to move the mouse a tiny bit and then move it back to where it started every so often. The whole maneuver should take under a millisecond.