They way to keep them dwarf-ish is to remove any leaves that start their way up to the surface. You can see the difference between regular leaves and wanna-be lily pads, and should remove the latter quickly.
Once the lotus has figured out that up there is more light and CO2, each leaf will go straight up. You might be able to revert that by removing all leaves. Hopefully that will give lotus a big scare and it'll start growing nice compact leaves again.