By default, there's no way to change this. The hotspot IS the center. Maybe in future releases of C2 will the hotspot be editable as well as the add of points (like in CC).
But as of now, you would have to replace manually any reference to Sprite.X by (Sprite.X - Sprite.Width/2) and Sprite.Y by (Sprite.Y - Sprite.Height/2). This is longer to write, but you would achieve what you expect.
Once again, instance variable is a variable contained by your object but with no direct affect on it.