Actually, and I’m pretty sure about this, piano-ing doesn’t help in ST at all. If you tap alternating Fierce and Strong, you’ll get the Hand Slap out simply because you pressed ONE of those button enough times for it to register. And I think it’s 6 presses of one button within a certain time frame (later games would reduce it to 5, and then they would introduce the piano-ing possibilities even later).
If you are playing on a joystick, oftentimes I use two fingers (index and middle) for tapping one button, alternating. But if you are on a pad, I’m not really sure of any good techniques outside of just mashing like there is no tomorrow.