Having started this thread, I feel obligated to report a relevant observation. I just had a barb city form where only 6 of the 9 tiles were in the fog of war. (The center was in the fog of war, but three tiles near one of my cities were visible to me before and after the city's spawning: I reloaded to confirm.) This would imply that for this strategy to work, you'd have to have blue circles exactly where you want them and keep only that blue circle (in the general vicinity, of course) under the fog of war.
Of course, the bigger problem with this strategy is that only rarely do I find that I agree with the blue circles these days.