title: Implement two sortable lists in jquery-ui where one is hidden and is revealed after dragging over the title
body: <p>I have two sortable lists linked together using <code>jquery-ui</code>.  One is hidden however and I'd like it to be shown when dragging an element from <code>List 1</code> over the title <code>List 2</code>.  Then without releasing the mouse, I'd like the elements in <code>List 2</code> to continue to sort.  </p>
  
  <p>The reveal does work, but the elements do not sort once the list is shown.  How do I go about implementing this?  Here is a link to the <a href="https://jsfiddle.net/k19zsa2g/5/" rel="nofollow noreferrer">js-fiddle</a></p>
  
  <p>To see what I mean, try dragging <code>Card 1</code> to the title <code>List 2</code>, and then to <code>Card 4</code> without releasing the mouse in the fiddle</p>