Putting a Stainless Stone in the bucket is a pretty good thought. Similar to what is done in a lot of breweries where they will use a CO2 Lift.
However, because a stone is designed to create very small bubbles. . . you won't get the degree of turbulence that a production brewery would get with a CO2 Lift. CO2 Lifts are done typically in the dump port (very bottom) and rely on large bubbles to churn the wort.
The Bucket doesn't lend it self to putting a Port on the very bottom. . .
And if you over use CO2 during dry hopping. . . you will scrub the aroma.
Hope that helps