Could you not just put a page before entering the website in a similar vein to the alcohol websites. In this case saying Users residing in the USA are not permitted to use the content.
Doesn’t really work though, as a banner page can’t STOP the US folk accessing it [well it could, but it would be tricky and ugly]. Also, that kinda stops half the trade done on the internet. Also, if the US pass it there’s then pressure on other countries to do the same.
Really it’s far better if they’d all just get a grip.