[sallen]

The idea of a bellypan extension is a very good idea in my book. I am thinking along the same lines for my Golf.

Many aftermarket "splitters" are available with tie rods, so you could buy a boy racer type rear splitter from your local tuner and extend it (that's what I intend to do). My thinking is that it will add a tiny boat tail effect to the air coming from under the car, in a similar way that a small kammback esque spoiler would for airflow going over the car.

With the tie rods you could adjust the angle until you get most gain.