I have one on the way, but my welder had both hands operated on. No wonder, 30 years of puddling stainless welds.
Using a floor plate and seat stand:
https://www.springfieldgrp.com/products/taper-lock-series/pedestals/manual-adjustable-pedestals
The seat swivel comes off, that's where the knee/lap yoke will be, used a flat floor plate.
https://www.springfieldgrp.com/products/taper-lock-series/taper-lock-bases
Will post pics when it gets home from the welding shop. Basically like an aluminum drift boat rest. You might give FishOn Fabrications a call or email, they are sponsors here. https://www.fishonfabrications.com/