older post so maybe you found it out already, but I have the answer for you how to get duckfoot leaves.
been breeding with it myself for a while now, and it's a very easy trait to select and stabilise.
it inherits as a simple single recessive gene.
so crossing a plant with duckfoot leaves with a plant with normal leaves will never give duckfoot leaves in the f1, but all f1-plants will be carriers.
inbreed f1 plants with eachother, and 25% of the f2 will have webbed leaves(visible from the 2nd-3rd set of true leaves, so you can kill any non-webbed very early, saving space). since it's a recessive, once you have done that selection, and you cross webbed plants with eachother, all offspring will be webbed.
I find it's also a handy tool to check pollen contamination. since I only grow outdoor, sometimes I get some contamination with pollen from other people. however, I'll notice immediatly since I will get non-webbed plants out of the seeds I made, and I can just kill the non-webbed plants and the leftover webbed plants will be from my chosen, webbed parent.