Generating Flattened Outer Outline

I am sorry in advance for asking but I’ve been wondering for quite a while how to do this.

I came across this example before:

This creates a flattened view of a 3D mesh but what I need is only the outer vertices, so when applying skin to them afterwards you would get something like a cookie cutter mesh.

If there’s a simple solution around, I’d be very glad to hear about it. Thank you.