They aren't called "meal worms" for nothing. Just about any cereal grain will do. I see no reason not to use the farina unless someone reading this has found it to be unsuitable. Common sense indicates it should serve the purpose of substrate. Give it a try and let us know how the worms do. If they grow and pupate, you will know it's working. Don't forget to include sliced veggies for a water source, and try to keep it out of the farina so it won't gum it up, since there's going to be considerable gluten in it.