For what it’s worth, here is what the finished board looks like.
I drew the outline of the left half of the butterfly in Inkscape. I exported a DXF from Inkscape and imported that into the Edge.Cuts layer. For the filled copper zone (darker colored area), I exported a bitmap from Inkscape and then converted it to a zone using these instructions. The exposed copper markings on the wings were created by importing another bitmap into the soldermask layer.
I then created a mirror image of all of these (the board outline, the copper zone, and the wing markings) using my Perl script, to complete the right half of the butterfly.
