Take a picture of the plate and "Shrink" it down in photo shop or something similar. then just cut it out and mount it.
OR...... take the real plate and "crunch" it up. Then all you have to do is paint a bunch of squiggly lines on the model plate and crunch it up too.
If the police pull you over for having an unreadable plate just tell them your a modeler....... It should be fine....