I spread a group of the Winter leaves on a dry, folded, paper towel in one of those clear, ventilated plastic containers berries are sold in. So far, about 100% every time. Once plantlets form I move them in groups to community pots with slightly damp media sealed in ZiplocŪ bags, then moved into individual pots once they have grown a little larger.
Very strong fluorescent light is helpful once the plants are moved into the ZiplocŪ bags to avoid damping off and to support strong growth. It is also essential for continued vigorous growth to blooming size plants.
Here is a photo of a group of Pinguicula gypsicola plantlets created using this technique. These are several months old, after the plantlets have formed. If they are moved to community pots as soon as possible after the plantlets form the young plants will grow with maximum vigor to larger sizes. Those in this photo will grow more slowly to larger sized plants:
You can tell by the dry, dead, remains of the parent leaves that these were not produced from Winter form leaves, but rather by Summer leaves.