The VGs actually seem to work in their current location. Tufts show good straight flow over the entire rear window.
The flow without the VGs reminds me of the new Beetle, which also has a Cd of .36. I'm sure I can get it down to .32 with just the kammback.
However, I haven't noticed a change in fuel economy with them on, and I'm sure testing won't show a noticeable difference. I'll definitely be going with a kammback. I need to get a hold of the sign shop again, because I haven't heard back from them yet...