Outdoor antennae on a plane present a pretty good windload (area x windspeed). Aside from the cool DIY factor, cantennas often aren't very good antenna, they are often the wrong size (it seems I read somewhere that Dinty Moore Beef Stew cans are much better than Pringles, wavelength-wise). It would take a lot of tape to keep it on. Did you check out the original link? There are some more pics there.
Yes, the higher speed and high altitude blurs GPS accuracy a lot. Re-driving/flying an area would let you get increasing averages that are better and better each trip. Let us know how it goes, and give us pics!