All of this will wait patiently now, until you are ready for it, and the soup will be the better for the waiting. When that time of readiness comes, you, or the recipient of your generosity, simply need to reheat the soup and drop in the greens. Separately heat the meatballs up, in the oven or in a skillet on the stove. When the greens are nicely cooked, about 7 minutes, taste the soup for seasoning (it should be pretty subtle, as the meatballs pack a wallop), and divide it among the bowls, dropping a little cluster of meatballs into each serving.