I haven't tried it for homebrew but know this method is used commonly in some commercial breweries.
The millions of tiny bubbles generated by the stone are effectively increasing the surface area of the CO2 in contact with the beer. (same as O2 diffuser ) This increases the rate of absorption so in theory you should be able to carb faster.
I've thought about rigging up a diffuser stone onto the end of a liquid dip tube. Cold crash the beer. Seal the keg then set the regulator to carbing pressure. Give it a day and swap to a gas inlet tube.
Never got around to it but it is still on my want to do list.