I have changed the wiper arms and blades on my focus to 'aero' flat blades with the wiper arms from a VW Polo (approx 2001 to 2005 years I think). They now sit well out of the airflow with only a small part of the arm visible when looking up the bonnet line.
Als this company
Ford FOCUS 1998-2001 / 2001-2003 - JDL bonnet extension - www.jdltuning.com makes a bonnet extension that will fill the gap and direct airflow over the blades. Looking at the images though I think it may kick the airflow up at too high an angle for improved aero??