For the Hydrocotyle type plants, and even some of the hygrophila species, keeping them creeping takes some maintenance every couple days.
Highlight, CO2 etc, can make it easier, but what really works is continually burying the growing tips. Every time the growing tip emerges from the substrate, produces a leaf node, and then keeps growing. Bury that growing tip. There are many plants that respond to this treament that are more traditional ground covers, Glosso, Elantine triandra, E tennelus, Ranalisma rostratum etc. Keeping the growing tip burried even helps these plants form a better carpet.
For stem plants, like Hygro species, you can use the air roots, as each node drops roots, bury those roots. Though I have only done this with hygros, I bet you could do it with other stem plants.