Do you have substrate of any sort? Gravel or sand? Don't plant as a clump but as individual plants and it will fill in. Alternatively, if you don't have substrate, you can plant it in a tiny decorative ceramic or clay pots with sand or in weighted-down craft mesh. With the craft mesh, rinse them thoroughly in dechlorinated water, poke individual plants in the holes and weigh the craft mesh down with rocks covered in moss. You will need to fertilize with a liquid fertilizer or, if you have substrate, with root tabs.
It would take forever for them to take over the tank but the craft mesh would contain them.