Um...So let's say someone with the spiffy custom plate you want smacks into another car and drives off, and their plate number is taken down. The next day, their time runs out, and the plate rolls over to you. Later that same day, the cops check up on the plate number that some civilian reported as a hit-and-run, and they come up with your info...whoops.

Ok, so not very realistic, but it's an example of why that wouldn't work.