allora prova cosi:
MovieClip.prototype.pulsante = function() {
this.onRollOver = function() {
trace("pippo");
this.gotoAndStop("rollOn");
};
this.onRollOut = function() {
trace("pippo2");
this.gotoAndStop("rollOut");
};
};

usa cosi:
_root.mc.duplicateMovieclip("mc"+i,i);
_root["mc"+i].pulsante();