I made a basic waist reversal LORA. This is a pretty niche fetish but I thought some might enjoy messing around with it. Even if you're not into it, it's still hilarious. A value of 1 seems to work in most cases but if it's giving you trouble due to a layered art style or strange pose, try increasing the value to 1.2 or even up to 1.5. I used a diverse set of references to include many art styles, 3D renders, and photo realistic, so increasing the value shouldn't affect the style.

It's my first LORA so I'll try to improve and update it.

If you want a version for Illustrious, here's one by Cikin (It works just as well in my testing): https://civarchive.com/models/1364790?modelVersionId=1541919