It's impossible to block U.S. players who want to gamble using Bitcoin. U.S. regulation on gambling is at a bank level. The popularity of Bitcoin gambling definitely stems a lot from the fact that U.S. gamblers cannot use their U.S. banks and debit cards to online gamble. There is also somewhat of a gray area in general as banks and traditional financial networks are not involved in Bitcoin gambling sites, just as taxation is still undefined for many.
I don't want to do it =/= impossible.
If you verified your customers are non-US then you would be compliant with US laws. If you don't claiming it is "impossible" won't be a defense. Not wanting to verify your customers to comply with US laws doesn't make it impossible.
Something of interest, some U.S. based data centers when I approached them for information accept Bitcoin Gambling sites, but not traditional gambling sites. Although I wouldn't recommend anyone to host in a U.S. datacenter none the less even if there is an overwhelming amount of options when it comes to U.S. based hosting.
It is all still a gray area like the majority of Bitcoin. To start a regulated gambling site handling fiat monies and payments, requires very expensive licensing in the many jurisdictions around the world that offer gambling licenses. Right now that does not exist with Bitcoin.