I do not remember P5 - maybe there is no this option.
In P6 and P7 make 2 simulation:

1. skirt collide against all necessery body parts.
   2 when sim_1 is calculated make sim_2 for robe checking body parts (you can not check hip and maybe buttocks) and checking skirt.

Ofc both simulations must have the same frames to move together.

If it does not work search special offer on contentparadise - you have 3 days to get P6 for 30$.