Help with listing pages in sidebar

I’m trying to setup a secondary navigation through sections of a wordpress site. I’m currently using wp_list_pages() and it’s mostly working the way I want:

<ul class="lft">
  <?php
  wp_list_pages('depth=1&sort_column=menu_order&title_li=&child_of='. $categoryid ); ?>
  </ul>

The problem is, I only want the depth to show the current page. So using the above, if the current page has deeper child pages those don’t display. How can I make the menu only display child pages of the current page, but sibling pages of the current category?