Still, exotic concoctions will net you very little. Best to use a substrate that naturaly winds up having the right moisture content. The only problem with pop corn is that it will never absorb enough moisture to enable you to get the full nutrient value from the stuff. If you manage to get the inside of the kernel wet enough, the slime it produces on the outside promotes contamination. If you don't, your corn will dry before you manage to get a great final yield. Still, overall rates are quite good. Rye is your second best but it takes some experimenting to get to the point where the kernels don't burst. Best bet to cheat here is to use gypsum, it will absorb the excess moisture and tweak your PH a bit. The reason no one is offering more suggestions is most likely because there aren't any really.