I actually made a guide how on my tumblr!! :D (though I think it's a bit sloppily put together!)
https://arcadekitten.tumblr.com/post/730014096258416640/how-i-created-a-dress-up...
It's simple once you get the hang of it, I just figured that using RPGMaker's commands it shouldn't have been too hard to use images as tools for dress-up! ♡