DO NOT BLOCK UDP! Doing so would prevent name resolution and likely interfere with any online games and many other applications. Basically you could do nearly nothing with your internet without UDP.
Mircea is right that bandwidth limiting/throttling would work well. This could be done from within his torrent application or from the router if it has a quality firmware (consider tomato and dd-wrt 3rd party firmwares if the stock does not support those QoS features).
pirate in web results would only block those sites. He could still get torrents from other sites.
Blocking the popular trackers would probably work well but peer exchange may circumvent that and blocking like that is a pretty dick move either way.