That will be interesting.
The challenge as I see it is that they were creating fin geometry dynamically based on the geometry at the silhouette. Without c++ code, you may have to be creative and use the use built in mesh splines somehow. Or use some kind of pivot painter like painted logic with UVs or vertex colors so the built in strips know the width/position of the tree at all points. Or somehow virtually shrink the geometry using virtual coordinates for the main trunk so you can use the edge as a virtual plane for the fins. Lots of things come to mind to try but they all seem to require a lot of work.