Morphs. ERC morphs on the clothing controlled by the joints of the figure are the way to have it done automatically. If twer that easy, we would be awash in them. A conforming skirt is difficult. One of the main problems is the IK chain requirements. The R buttock cannot touch the L buttock, nor R thigh, L, nor R shin, L. Hip or some neutral must separate them. The intervening group does not move with either leg. Sitting would be a particular problem because both legs would be horizontal and the hip between them vertical - straight down from the groin. As for a morph to move the hip section: the sort of morph that I find most difficult to do is one that is a hinged rotation. The fact that modeling programs have rotation functions, seems like it should be easy. Unnn-fortunately, in my experience, the morph is OK at 0.0 and 1.0, but the verts go really distorted in between. They must be pulled instead. A prop moulded in the sitting position is probably the simplest way around this.