My gut reaction would be to recommend a simple clip-in surround that's in the same style as the bezel above it. I'd bet you could produce a basic shape with some welded-up ABS or the like, and use your shaping skills to get it to look like it was designed to be there. A second option might be a flip-down cover panel, but if you actively use the unit, that's a poor idea.
Just to be sure you hear it enough -- that bezel is absolutely beautiful work, in a league with turbocad6 and Nexson. And I appreciate the detailed explanation of the process you used to get from OEM to way-better than OEM. Excellent design job + excellent execution = Wow!