This is a very old thread, but I figured it couldn’t hurt to answer it for someone else.
The only thing I can think of is using a second drawing with a black line and color fill on the Color layer, and use that Color Layer to cut the main drawing. The black line from the Cutter drawing would appear to close the shape while the Color Layer would effectively mask out that chunk that you’re cutting out of the circle.
So in your example, you would use (in the Network/Node View):
a Color Art module from the Cutter drawing to cut the circle
a Line Art module for the Cutter drawing, which is inversely cut by the circle’s Cutter
The inverse cutter needs to be plugged into the main Composite to the left/in front of the circle cutter in order to show up
You can create a simple shape for your cutter drawing, say a triangle or square, and put an envelope deformer around it. Then it will essentially work like a mask in After Effects, and is totally animatable.
Nevertheless, I think it would be great if there was an independant “Auto Outline” effect module creating a resulting unique proper pencil line with soft line width variation and texture.