Display Author Specific Categories

Please may I ask for assistance on this issue:

When viewing a specific author, in the categories sidebar widget I would like to display only the categories that that author has posted in, not all the categories on the site.

please see website here: http://www.fuzegraphics.co.za/demo/musika/author/fuze/

Does anyone know if there is a plugin for this or which files I need to edit and how?

Below is the current widget that is displaying the ad categories. I presume all i need to do is change the way this widget pulls information:

// widget to show all ad categories
function cp_ad_cats_widget() {
?>
<div class=”shadowblock_out”>

<div class=”shadowblock”>

<h2 class=”dotted”><?php _e(‘Ad Categories’,’appthemes’)?></h2>

<div class=”recordfromblog”>

<?php wp_list_categories(‘orderby=name&order=asc&hierarchical=1&show_count=1&use_desc_for_title=0&hide_empty=0&depth=1&number=&title_li=&taxonomy=’.APP_TAX_CAT); ?>

</div><!– /recordfromblog –>

</div><!– /shadowblock –>

</div><!– /shadowblock_out –>

<?php
}
$widget_ops = array(‘classname’ => ‘cp_ad_cats_widget’, ‘description’ => “” );
wp_register_sidebar_widget(‘cp_ad_cats_widget_id’, ‘CP Ad Categories’, ‘cp_ad_cats_widget’, $widget_ops);