I've always had a difficult time with hip articulation, even with the rebuilt matoran. I'm long out of practice building, and don't have all the parts to test the feasibility of this (the thin, single-axle waist annoys me). I don't have any of the custom parts packs, so this is desperately non-inika.
If any anon's interested in improving it, here:
https://www.file.io/S7tf/download/G2jgnXEOwO4g