I’ve used inflatable gags and plugs, but that isn’t the same thing.
I’ve frozen water balloons with the keys to cuffs inside them, making a time lock.
I’ve seen balloons with helium attached to nipple clamps and the like, more for aesthetics than anything else. I don’t know how many it would take to generate real tension.
Oh… I’ve got a fun game.
Take several balloons and fill each with something.
One will have uncooked rice in it.
One will have a key to your restraints in it.
One will have ginger root in it.
Some may have rolls of paper with tasks on them.
you wouldn’t be able to see what is in each, but they would be numbered.
Perhaps he would make you crawl to the number you choose, bring it down and pop it, then you would have to suffer whatever is inside, based on your choice.
Uie's Cage 