Found this at Lowe's Pro Connex part number 49151 in the electrical aisle. 3/4 in knock out plug. Tweak the tabs a touch and it fits like a glove. Cost all of $.36
Someone did this with a plastic furniture cable hole plug but they glued a round Honda emblem on it. Made a really nice center cap. Can't beat the price, right!
Definitely not the end result, but a good solution to what to use for a base. Doesn't look bad by itself, though.
I had a bike with a honda logo on it. then I got the tire change and they balance it with something in the hole so off it had to come. PO had used some sort of putty to span enough of the gap to hold it in place and it took me half an hour to get that shit off my wheel. I like the hole. It's just fine.