Here's a link to a technical drawing for your car.You could use the Aerodynamic Streamlining Template tool near the top of the Aero.Forum page to see the comparison.
If you're not ever going to elongate the car I don't know if the fast-back conversion would show a significant advantage over VW's optimized aero-back.
http://carblueprints.info/blueprints...-passat-b5.gif