Smooth the soil on the top and lay the leaves on it face up and spaced so they don't quite touch each other. Take a pencil or other small object and mound up a tiny bit of soil over the place where the leaf is broken. Then sit the pot in a tray of water until the soil on top is moistened. Then put a propagator cover over the pot and place it in a shaded area. Sow the seeds and raise the seedlings in the same manner that I have described for the north american pitcher plants, except note that butterwort seeds do not require a stratification period.
Division is the only really good method for propagating bladderworts.
Once a clump has reached suitable size it is very easy to pull apart into several sections which can be repotted and will continue to spread across the pot. Simply sprinkle the seed into pots with the same soil and conditions of the parent plant. Also bladderwort seed is very tiny and often if the flowers are allowed to go to seed you will find many little bladderworts sprouting up in all of the pots that border your bladderwort pots. Young H. nutans. Division can be carried out when the plant has formed a clump with at least 4 or 5 different growing points.