I would guess the process you mentioned might be the only way to reduce and slow it's growth, though of course perhaps keeping it a bit drier and less fertilizer perhaps?

Hi
Do a search on the family there are at least a dozen other members bedides mimosifolia. Some mature at under 5 feet. There are also some hybrids with different colors.
Finding them would be difficult though gary

Huh! My Japanese BF keeps ALL his trees short! Insane pruning will do it! :) You'll often hear me say "Put the shears down and step AWAY from the plant!" Hasn't the man EVER heard of SHADE trees?
I used to have before and after pics of some insane pruning to shock people... I was SURE the plants would die.... butchering a bush from almost 3 feet down to a couple of inches!!! But the poor thing is still surviving.
He keeps his fruit trees very short, which is nice for picking.
I am not a fan of plant butchering, but I guess you can do it.

You really can't restrict a tree's growth with plunging a pot. The pot needs a hole in the bottom for drainage. The tree's taproot will find that hole, go through it, and establish an entire root system outside the pot.
As mentioned above, you can hack the tree back, but you might not get flowers in doing so. And if you aren't going to get flowers on a jac, what's the use of planting it? Maybe you should consider a Guaiacum coulteri or some other blue-flowered shrub that will stay smaller.