You don't have to use the remote out wire. You only need to supply +12v for the acc and battery lines. If you are going to use your ATX power supply for this, you can use the yellow wire on the molex connectors coming out of the power supply. You can also use the ground right next to the yellow wire from the same connector.
So on the screen power connector, the yellow wire from the molex connector will be connected to both the acc and battery lines. The ground line.... I'll let you figure it out.