You can't really do anything like that for a continental belt, there's no heraldry of a single country you can take. You could re-design the US title into something in the same vein, there's probably something official with an eagle on it that they can use instead of a flag. You can put that inside the same boarder as the UK title and be good.
Thinking about the belts a bit more, I'd like a North American title to look like the Intercontinental one. Take away the 'heavyweight wrestling champion' bit and make the map a bit bigger. Then for a series of regional belts you just zoom in a bit on the map to the required continent. Keep them all on white leather too. And no flags, 'cos they look really cheap.