Foams are indeed very sensitive to the structural properties of the materials present. I can't say what exactly in the cocoa powder prevented it from whipping, but no, if it doesn't beat up to a foam, then you can't make a foam out of it. Or rather, if there is any way of making a foam, one would have to hope that the problem is repeatable and then invest dozens of hours to make new batches to find out what exact conditions can make it whip again.
If you don't like the idea of wasting food, consider making something else out of the mass. Pancakes would be a great choice, as they tolerate a lot of changes to their batter, but also simple loaf cakes or muffins. In any case, it should be a one-bowl recipe, not requiring a complex combination method. In such recipes, you should be able to get away with the missing egg yolks, expecting some change in texture, but still getting it edible; just take a recipe, subtract what you already have in the mass (1 eggwhite corresponding to 2/3 of an egg) and add the rest of the ingredients. If the recipe doesn't originally expect cocoa, you can subtract it from the flour, as long as it leaves a substantial amount of flour in the end product. The fact that you warmed the mass shouldn't have negative effects.