I poked around the King Arthur Flour website for tips and ideas. They sell food grade cocoa butter for making chocolates - but they also said it's good for stiffening icing.
Anyone have experience with this? I'm intrigued. I've had good success making classic cooked buttercream with just butter, but it's true, it can get runny. I don't want to put Crisco in and ruin a classic buttercream with hydrogenated glop. This sounds like a good compromise.