This 3 hit combo is probably useless, and you will find very little use of it in a real fight. The only use of >b is the >b combo (which is awesome), needle combo, or just interupt move. If you must use it, you just do the short hop double fair normally, and add the >b in between the two fairs, you gota do it fast though.
Also, since the >b move doesn't give the opponent lag, they can hit you right after it if you don't react quickly, thats why this combo is rarely used. The >b combo is a different story since its fast.