You need pollen to pollinate. Whether the flowers are open or not is not important, as long as you have some pollen. By that line of thought, if you do have an open flower near by that is producing pollen (look at the stamens), then use a soft brush or qtip to move it from that flower to other open flowers. You can also open other flowers that are on the verge of opening by using tweezers, and then using collected pollen (from your brush or qtip) on them.