I found the answer here.
I modified it slightly to clone the row, instead of adding widths to the original:
helper: function(e, tr)
{
var $originals = tr.children();
var $helper = tr.clone();
$helper.children().each(function(index)
{
// Set helper cell sizes to match the original sizes
$(this).width($originals.eq(index).width());
});
return $helper;
},