Before I get started...I'm an aero-nub, so go easy on me.
Is the drag created by the VG's more a function of the frontal area, which was determined to be about as much as a small mirror, or the acutal areodynamic effect caused by them?
If it's the former, then I wonder why not consider a VG with virtually no frontal area. When I was an AV-8B Harrier mechanic, the VG's on the wings of those aircraft were esentially aluminum tabs bent at 90 degrees and riveted to the wings at what appeared to be, by eye, parallel to the direction of forward flight. When we broke them off, which happens when you climb on the wings from time to time, the Airframes shop would simply bend up a new one out of scrap aircraft aluminum and re rivet them back on. I imagine for testing, double backed tape should work, though the tape would have more frontal area than the tab itself.
Here's a link to a photo of a Harrier wing where you can see the arangement, size and spacing of the VG's on the wing. If it matters, the harrier is sub-sonic so any aerodynamic design of the aircraft wouldn't/didn't include sonic compresion...or whatever you call the sonic boom, so the VG design isn't compensating for anything super-sonic;
The VG's on those things are rather small, something like 1.5" long by maybe 3/4" of an inch tall...I'm trying to remember, but it was a decade ago.
Anyway, that was all a long winded way of asking if the drag is caused by frontal area, or the generated vortex following the VG's.