First, I didn't know about that circle trick. Thanks that's good to know.
Second, sorry, I know of no way to create odd-shaped regions.
Third, I don't know how your map is set up so this may not help at all, but WE can read terrain type so if you're clever enough with your terraining you might be able to set up a condition that picks a random point in the regoin and then checks if it's the right terrain type. If the terrain type is wrong than pick a new point - thus a functional odd-shaped region. Again, there are countless scenarios where that wouldn't work the way you want it.