Large flag mount brackets for a car?

I find after this election that I have an unexpectedly pressing need to wave large obnoxious flags from my sensible fuel-efficient subcompact while I drive.

Has anybody got models, templates, suggestions for how to mount a stout pole to a hatchback? I’m thinking of some kind of tube on a short arm that I could close the rear passenger door or the cargo door on to hold it in place.