help with sub movieclips appear/disappear

Hey folks, looking for some early feedback. So in a large movieclip that I drag, I have sub movieclips. Due to them being large they cause the drag/flick/scroll get clunky at times. So I thought about dynamically loading them depending on where the main movieclip is based on a Y state. So this seems to work BUT before I go down this long road, there has to be a better way do this. I've bolded the way I'm planning to go about it.

function mouseDownHandler(event: MouseEvent): void {

  TweenLite.killTweensOf(main);

  y1 = y2 = main.y;

  yOffset = this.mouseY - main.y;

  yOverlap = Math.max(0, main.height - bounds.height);

  t1 = t2 = getTimer();

  main.stage.addEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);

  main.stage.addEventListener(MouseEvent.MOUSE_UP, mouseUpHandler);

}

function mouseMoveHandler(event: MouseEvent): void {

  var y: Number = this.mouseY - yOffset;

  //if main's position exceeds the bounds, make it drag only half as far with each mouse movement (like iPhone/iPad behavior)

  if (y > bounds.top) {

  main.y = (y + bounds.top) * 0.5;

  } else if (y < bounds.top - yOverlap) {

  main.y = (y + bounds.top - yOverlap) * 0.5;

  } else {

  main.y = y;

  }

  blitMask.update();

  var t: uint = getTimer();

  //if the frame rate is too high, we won't be able to track the velocity as well, so only update the values 20 times per second

  if (t - t2 > 50) {

  y2 = y1;

  t2 = t1;

  y1 = main.y;

  t1 = t;

  }

  event.updateAfterEvent();

  if (main.y < 30) {

  main.OFbandTWO.visible = true;

  } else if (main.y < 20) {

  main.OFbandTWO.visible = true;

  main.OFbandTHREE.visible = true;

  } else if (main.y < 0) {

  main.OFbandTWO.visible = true;

  main.OFbandTHREE.visible = true;

  main.OFbandFOUR.visible = true;

  } else {

  main.OFbandTWO.visible = false;

  main.OFbandTHREE.visible = false;

  main.OFbandFOUR.visible = false;

  }

}

function mouseUpHandler(event: MouseEvent): void {

  blitMask.bitmapMode = true;

  main.stage.removeEventListener(MouseEvent.MOUSE_UP, mouseUpHandler);

  main.stage.removeEventListener(MouseEvent.MOUSE_MOVE, mouseMoveHandler);

  var time: Number = (getTimer() - t2) / 1000;

  var yVelocity: Number = (main.y - y2) / time;

  ThrowPropsPlugin.to(main, {

  throwProps: {

  y: {

  velocity: yVelocity,

  max: bounds.top,

  min: bounds.top - yOverlap,

  resistance: 50

  }

  },

  onUpdate: blitMask.update,

  ease: Strong.easeOut

  }, 2, 0.3, 0.5);

  blitMask.bitmapMode = false;

}