A bit of a hack, but you can provide a label for the column and
pass it to this method. This order can then be passed to your comparator.
I am sure there are better ways, but this at least gets you the column sort order.

private Ordering getColumnSortOrder (String columnLabel) {

 FacesContext facesContext = FacesContext.getCurrentInstance();
 HtmlDataTable htmlDataTable = (HtmlDataTable)facesContext.getViewRoot().findComponent("formId:tableId");
 Iterator<UIComponent> columns = htmlDataTable.columns();

 while (columns.hasNext()) {
      HtmlColumn column = (HtmlColumn) columns.next();
      String label = column.getLabel();
      if (StringUtils.equals(columnLabel, label))          {
           Ordering order = column.getSortOrder();
           return order;
      }
 }
 return Ordering.UNSORTED;
}

Hi Anthony,
I also need same funtionality. I am wondering whether you are able to resolve this issue and how?

Siva