Emulating dynamic PShop "stamp" or "clone" effect in AE?

I'm erasing a "badge" on the back end of a station wagon in some moving footage.

What would make this a breeze is if I could tie the color of the masking solid to a sampling area near the badge, so that the color of the solid changed to match as the car moves from shadow to light and back.

I can animate the color of the solid by hand, but what a PITA. It'd be better to automate the process, and more generally useful.

What would be the method? There'd have to be some sort of way to sample the image at an animated point, and then use expressions to get the color into the Solid. So, some kind of "eyedropper" effect.

Thanks for any illumination.

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