It's a little tough to do. One of the "contact buttons" is indeed at chassis ground, but the wire running to is on the body side is about 8 inches long. This is okay, but it appears to be number 16. You can take the trim off an install a braid instead, but like I said it takes a lot of work to accomplish. Is it worth doing, maybe. Every little bit helps, but you might not be able to measure the difference.
Maybe just as important is grounding the radiator shell (for RFI egress reduction). Thankfully that task is much easier to accomplish.