I've never seen a how-to either. This is a quirky item that not a lot of people have done. I'm going to be building one myself, but I don't imagine it will be very tutorial worthy. As always, how do you say "take your clay and shape it to look like that, then make a mold of it" in a useful way?
I free-hand sculpt most of what I do, so there aren't many found items / easy to duplicate things to be shared.