Ah ok that makes sense.
Basically you want to put objects around the edge of the object and want the objects to be angled in the direction of the edge.
There isn't a way to access the collision polygon. A way to approximate it could be to create a ring of objects around the ground then move them toward the ground's center until they collide with the ground. At that point the object's will be shrink wrapped around the ground. You could then find the angle of the edge by using the angle expression between two adjacent points.
There are probably other ways to detect the edge. One could be to position invisible rotated rectangles around the shape in the editor to define the edge. You could also use the paster object to draw a Sprite in a warped way around the shape.
Unless you're drawing the ground at runtime it's probably better to position the objects in the editor. I believe Sqiddster did that in Airscape.