If you're running windows you might check the video drivers you're using to see if their is a Mirror option.
You didnt state if you're driving an arcade monitor or a TV or a computer monitor, but in essence, on all three, with varying levels of possibility (TV/arcade monitor = simple, computer monitor: maybe, maybe not) you can simply flip ONE set of yoke wires (either horizontal or vertical--not both, as that rotates 180 degrees) to produce a mirrored image.