I do them at the Wyrmres Temple, too. There's a ledge above the flight path. Don't need to jump, don't need to worry about where you land, just walk off, and away you go. It's my favorite spot, since I can line up my toons, run forward on them all, and since I don't need to worry about jumping, or landing in the right area, I spam my guild with the achievement all at the same time