target the cpw_excerpt filter at a specific widget

gistfile1.txt

/**
 * This gist shows how to use the "number" attribute of a widget object to target a specific widget
 * You can find the number associate with a specific widget by inspecting the generated HTML for it,
 * it is the suffix of the id attribute of the element wrapping the widget
 *
 * @param string $excerpt The current excerpt
 * @param WP_Widget $widget the widget object from which it is possible to get the information of its type an dID number
 * @param int $length the configured request length for an excerpt. A zero is passed if no value is actually configured
 * 
 * @return the widget number appended to the excerpt
 */
function cpw_excerpt_filter_wn($excerpt,$widget,$length) {
    return $excerpt.' '.$widget->number;
}

add_filter('cpw_excerpt','cpw_excerpt_filter_wn',10,3);