No hammering in the traditional sense.
You just have to hit each note hard enough with the left hand so that you don't have to pick it....i suppose you could call that a hammer-on, or whatever.
Either that, or you get so used to hitting the bar that you barely even have to hit the note with your left hand to get it to ring.
Like I said, the force of your hand hitting on the bar will make the notes you fret resonate clearly. But that takes some time, and some getting comfortable with the whammy bar...undertstanding exactly what you can get out of it, if you will.
There's no real tricks or anything here, besides taking the time to do it right.
Just learn to fret notes while hitting on the bar.
