it involves bon voyage gifts or something like that....very very time consuming and Carnival doesn't like it as it congests their server. Another board has banned its discussion as a result of problems stemming from that.
Holiday 5-day Western Caribbean
Liberty 8 day Western
You start ordering stuff to yourself on the Carnival website plugging in different rooms. When you get a response that's different from the others that is probably your room. I've never taken the time to do it but others say it works.