Serving Stocks -- locking stocks worn behind the small of the back (allowing for the wearer to hold a serving tray)
See the full gallery here: https://imgur.com/a/iMvrGqs
These have probably already been invented somewhere under another name, but this is my take on Serving Stocks. They’re worn behind the back, with the elbows through each hoop. This traps the wearer and limits the use of their arms, but still leaves their hands free to (awkwardly) do tasks like tidy up, or hold a serving tray (hence the name). (The tray works even better if you level it by adding the cheap y-chain nipple clamps, attach two of them to the sub and run the last strand up through their collar and back down to the front of the tray.)
The stocks also ‘improve’ their posture, forcing them to arch their back slightly, leading to more of a chest-thrust-forward-butt-thrust-back sort of pose, especially when combined with heels.