Sortable over both x and y axis

I'd like to be able to use Sortable to sort items in a list like this one:

<style type="text/css">
ul {
  margin: 0;
  padding: 0;
  width: 800px;
  overflow: hidden;
}
li {
  list-style-type: none;
  width: 180px;
  margin: 10px;
  float: left;
  text-align: center;
}
</style>

<ul>
  <li>1st item, on 1st row</li>
  <li>2nd item, on 1st row</li>
  <li>3rd item, on 1st row</li>
  <li>4th item, on 1st row</li>
  <li>5th item, on 2nd row!</li>
  <li>6th item, also on 2nd row!</li>
</ul>

As you can see, the 5th and 6th li are pushed to a second row, as they didn't fit in the first row of the 400px ul anymore. Currently, we can only use Sortable on lists that are either horizontal or vertical, not mixed ones like in this example.