In P4 you probably can't. In P5, convert the clothes you want to pile into obj objects or props then import them as props, clothify them in the cloth room over where you want to drop them and set the cloth/cloth collisions on and collide with the ground and the other stuff already on your pile. It will work on most things, though the odd piece of clothing is not open at the ends, in which case you might have to fiddle with the grouping tool before exporting as an obj or prop. Use about 30 drape frames (you needn't have more than 1 frame in the actual pic). Make sure you untick drape from zero pose for this, it only wastes time and will screw you up if there is anything that's a figure that you're colliding with. I've done some this way and they turned out quite believable.