stoner never did it till the raised his pegs higher.
the best answer ive heard, and believe, is with the GP shift you have to go under, so youre done banging out the gears, you move your foot out and back, but youre so hard on the brakes that sometimes moving back, your feet swings fwd under the G force, so it dangles a bit then somewhere along that time, you make a greater effort to put it back on the peg.
Now others will say, oh, but Rossi does it on both sides now, true, but Rossi also uses the rear brake when going into turns, so maybe in going from brake pedal back to the "toes on the peg" postition, the G force dangle kicks in.
Rossi ir weird anyway, he is one of the hardest and latest brakers in thebusiness, yet he brakes with 4 or 3 fingers at a time. How he boutbrakes others and gets back on the gas before them when using 4 fingers is a beyond me.