Erm... best initial guess is that it would best be done in the software, since you could swap X and Y pretty well in hardware but all that would do is rotate the image.
Since your vector image is really just connected points on an XY plane, you'd have to multiply all values by -1 to produce a mirror image, or else design a small circuit to change the direction of the signal voltages (i.e. 4v X to -4v X and 5.6v Y to -5.6v Y).
I could be wrong, that's just my initial guess at it.