Get a gallon size bag that has a "zipper" type closure on it, add about 1/3 bag full of pond water, put in the viviparous starts in the bag, float the bag in a sunny part of your pond, check the bag every couple of days & change the water as needed, & when the starts are big enough to plant, pot them in small containers with about 4-6" of water over the crown. Try to have the babies where they will get direct sunlight & no other lily pads crowding them. I've been able to kick start many viviparous pads/plants this way but there are some that don't survive either.
You can also do this same method for a healthy viviparous pad that has a well developed node, especially during the hot months. One key is the water temperature must be warm enough. I've found 1 pad per bag works better than crowding several pads into 1 bag.