I wrote a post a while back with some ideas for discreet public embarrassments.
And another post about ideas for humiliating self-punishments in private.
I think any good governess who was too busy to spank a wayward boy would probably produce a nice big butt plug and stretch the naughty boy’s bottom.
The plug would be likely be lubricated by something designed for the recipient’s discomfort, such as Icy Hot, Deep Heat, chilli oil or ginger paste.
She might even decide a good figging was required, with his underpants and trousers pulled up afterwards. With a belt tied around the waist to ensure no interference. After a couple of hours the naughty boy would be begging to have his shorts pulled down, begging for a thorough bottom inspection.
Just imagine what your imaginary disciplinarian would do…