Missouri last year passed a new law that provides for a 3rd plate specifically for this situation. The "plate" is actually just a piece of paper you tape in the window. But some people got stopped and ticketed, and approached the Missouri Bicycle & Pedestrian Federation, and we got it passed. It was the easiest piece of legislation we have ever gotten passed.
A lot of people wanted to know why we didn't try to get the law changed so that bikes obscuring the plate wouldn't result in a ticket. The answer is because that is seen as making police officers' jobs harder. The 3rd plate solution is a little inconvenient for cyclists-- you have to fill out a form, pay a fee, and when you get your $11 piece of paper you have to fold it & tape it into your window-- but there is no way we could have gotten an exception passed for cyclists.
I think AZ has a state bike/ped advocacy group? Sorry, I think you better pay this ticket, but tell the bike/ped group about it and let them know Missouri's experience. It's an easy win so it's great for the group, relatively low effort and then they can present it as a piece of legislation that they pushed through. It looks great on those fund-raising letters.
2009 Trek 7.2FX WSD, brooks Champion Flyer S, commuter bike