you can use Query Posts plugin which creates a widget that you can place on that sidebar, and select what to display.
if you are looking to code your own the its a you are sure that you wont remove it from that side bar you can create a simple custom WP_query to selset your post type and list them.
So you would need to change your code a bit like so:
<div class="block-3 border-top">
<?php
// A second sidebar for widgets, just because.
if ( is_active_sidebar( 'secondary-widget-area' ) ) : ?>
<ul id="secondary-widget" class="xoxo">
<li><?php //your query and loop here ?> </li>
<?php dynamic_sidebar( 'secondary-widget-area' ); ?>
</ul>
<?php endif; ?>
</div><!-- #sidebar -->
or you can just create your own widget and add it to the sidebar.
Hope this helps.
Ohad.