Best Way to Extend a jQuery Plugin

I just had the same problem trying to extend jquery UI plugins, and here is the solution I found (found it through jquery.ui.widget.js):

(function($) {
/**
 *  Namespace: the namespace the plugin is located under
 *  pluginName: the name of the plugin
 */
    var extensionMethods = {
        /*
         * retrieve the id of the element
         * this is some context within the existing plugin
         */
        showId: function(){
            return this.element[0].id;
        }
    };

    $.extend(true, $[ Namespace ][ pluginName ].prototype, extensionMethods);


})(jQuery);

hope this helps, please ask if you have any questions.