ok, for adding the div around the second level you will need to create a chunk for the template innerTpl like the following:
<div id="expand">
<ul[+wf.classes+]>
[+wf.wrapper+]
</ul>
</div>
for the javascript links you need to create a chunk for the template parentRowTpl like the following:
<li[+wf.classes+]>
<a href="javascript:toggleDisplayById('expand')" title="[+wf.title+]">[+wf.linktext+]»</a>
[+wf.wrapper+]
</li>
That should do it. Now the only problem you will have with this is if there is more than one submenu, it will have the same id as the first and cause problems. Also if a user has js disabled, the links will not function at all.