I kind of love commenter Paul Barwick's big idea:

arizonaplates.jpg
I propose we pass a state law here that says that any vehicle coming into our state with Arizona plates will be stopped and the passengers jailed if they cannot come up with papers proving their citizenship. Of course we deplore racial profiling, so we will demand that EVERY occupant come up with their papers, no matter their skin hue or ethnicity.

Might be hard to get laws like this passed at the state level. But progressive cities—places like the place Seattle likes to pretend that it is—should be able to enact laws like this one pretty quickly. Or, failing that, perhaps citizen arrests?