The trem shouldn't be able to go up much anyway. For the sake of string life (& trem life!) pulling it up much more than a semitone is not a particularly good idea - if the action is set to a half decent height then the strings "fret out" anyway.
Very few players actually tug right up on the trem either - most of those big harmonic squeals you hear on rock/metal records come from divebombing the trem, catching a harmonic while it's "down" then letting it back up to the neutral position...
just a semitone? weak.
try half an octave, then we can talk ;)
