For the Azureus / BitTorrent XML format, the document could reference the CC namespace and then implement the dc: and cc: prefixed tags accordingly.

see http://creativecommons.org/technology/metadata/implement

For the for the actualy BitTorrent protocol bencoded .torrent format, the dc: an cc: tags could simply be more bencoded dictionary items added to the main dictionary object of the .torrent file.

Examples:

8:dc:title12:Free Culture
9:dc:format10:audio/mpeg
This could also support complex relationships, given the URLs of related works:

Examples:

17:cc:derivativeWork50:http://www.example.org/freeculture.mpg.torrent.xml
9:cc:source50:http://www.example.org/freeculture.pdf.torrent.xml