sortable_element - dotted line property around drop target?

Hey - does anyone know how to put a dotted lined around the target drop point using the sortable_element? For example - those that use iGoogle - if you move your modules around you will see the target drop points noted with a dotted line before you actually release the mouse.

Here is my code:

<ul id="user_list">   <% for user in @all_users %>     <li style="cursor: move" id="user_<%= %>"><%= %></li>   <% end %> </ul>

<%= sortable_element 'user_list',                       :url => {:action => 'sort_user_list' },                       :scroll => 'window' %>

Thanks in advance!