$rss->add_module(prefix=>'my', uri=>'http://purl.org/my/rss/module/');

 $rss->add_item(
   title       => "xIrc 2.4pre2"
   link        => "http://freshmeat.net/projects/xirc/",
   description => "xIrc is an X11-based IRC client which ...",
   my => {
     rating    => "A+",
     category  => "X11/IRC",
   },
 );