I finally did a block of my 2013 Passat, but it's nothing I can show you because I put it behind the grille. It's just two pieces of flashing sitting in the frame member behind the bumper. I got the info on how to remove the grille here:
VWVortex.com - How to remove front grill?
It was just too difficult to try to find a cover for the outside that did not look seriously oogly. I understand it is not quite as effective aerodynamically. I suppose I could always tape some plastic on the outside there temporarily, for a long trip.
The bottom grille is just an area where I use some of that almost black gorilla tape, which allows me to adjust the opening size easily.