Make the entire skirt part of the hip group and use ghost body parts for the right and left thighs. Use morphs (or magnets)for lower part of the skirt to get any bending needed for the right and left shins. This allows the skirt to conform pose to the base figure for most poses. Use the morphs (magnets) for posing the lower portion of the skirt as needed for sitting and kneeling positions.

What figure are you making this for? I can probably send you a cr2 to use with the jp set up for the hip and ghost parts as I use them.