Experiment 1: I soaked a small leather scrap in water for over an hour. Then, I heated up some water to "almost too hot to touch" and put the scrap in for two minutes. There were no visible changes. Then I pulled it out and tried putting a curve on one of its flat edges. It worked just fine. Then I wrapped it around a pen to dry, to see how stiff and hard it would get.
Preliminary results as of last night: Surface finish has remained smooth, but the leather is just barely stiffened. It might have still been damp, so I'll check it again later. Also, after leaving it at room temp for most of the day, I relocated it to a heating vent overnight. Not exactly uniform warm drying, but at least it'll get periods of heat.
Problem: I really don't know what stiffness I'm looking for, and "live fire" testing is not in the cards.
Fabric mock-ups of different shapes (two petal, four petal rounded end): Fewer seams vs. better shape
Comparing stuffing materials (wool roving vs. something like rice or barley: Enough roving seems like it would make a lot of thread, but would a "beanbag" work?
Trying to figure out which leather stitch is the best option: Are abutted edges water-tight enough? How uncomfortable would seams be?
Ordering awls and needles from Tandy: I forgot that you can't just run this through the sewing machine (or even do it by hand without pliers)