Here is an idea for you. I just layed it up on one of my frames and I think it will look just fine. Make a sandwich out of two washers to catch the frame. Have the outer washer PC'd the exact same color as the frame.
I grabbed the washer that goes under the large center nut on the top of the triple tree. It is about the right size, thin and sits right into the existing recess for the switch. The OD is 1.415" and the ID .889 (it neds to be opened up just a hair bigger to pass the ignition. Could also include the little tang on both washers to capture the slot in the switch. Some adhesive bewteen the washers and frame and when you put it together and tighten it up and I'd think the extra washer would be barely noticeable.