Fill an area between two linked BLines

Is it possible to fill an area between two BLines, as shown in the picture (the area is pointed by green arrow) without manual linking of many nodes? The area is limited by two BLines. End nodes of one BLine (red) are linked with nodes of the other BLine (black).
Synfig Animation 2.png

It is possible. You need to do some smart blending to produce the effect and add two regions.

Notice how the red outline has doubled width.

fill-linked-outlines.sifz (2.25 KB)