You can use
THIS to block sites within Chrome, so you can block every download site for other browsers. You can also edit the
Hosts file (
Seen Here) to block URLs. Or, you can block sites in his router's settings.
edit: personally, I think the router option is the most effective and least annoying to do, so I'd go with that. The page should look something like this: http://i.imgur.com/voIJwuY.png