Or you do like Finland did, and order the largest ISP to block access to them. I hear Holland has also done the same. Will it hold? I am not sure. We don't have that many ISPs here, so something like this can work well.
http://thenextweb.com/eu/2012/01/09/...a-court-order/
You can also get ISPs to do this on an individual basis. When I worked at Qwest Long Distance, there were a lot of those pay chat lines they would not connect to because of the huge backcharges. Everyone on the network pays for those calls. Qwest would not route your calls to the "Backdoor to the Manhole" but AT&T would... Qwest service and rates were better.