Also see here for an example of doing it with surface control point editing:
http://moi3d.com/forum/index.php?webtag=MOI&msg=863.2

That technique involves making a starting plane that has a bunch of points in its interior instead of only 4 corner points, see this post for how to set that up:
http://moi3d.com/forum/index.php?webtag=MOI&msg=817.4

- Michael