A simple script for After Effects that adds an expression for Inertial Bounce to the scale property of the selected layer (as opposed to another script I wrote that affects the position).

Bouncer(scale)01.jsx

{
  //Begins the undo group
	app.beginUndoGroup("Add Inertial Bounce");

	//Global Variables:
	var bounceExp = "n = 0;if (numKeys > 0){n = nearestKey(time).index;if (key(n).time > time){n--;}}if (n == 0){t = 0;}else{t = time - key(n).time;}if (n > 0 && t < 1){v = velocityAtTime(key(n).time - thisComp.frameDuration/10);amp = .04;freq = 2.0;decay = 8.0;value + v*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);}else{value;}";
	var curItem = app.project.activeItem; //Creates variable that holds selected comp

	//Functions:
	function addBounce (currentLayer) 
	{
		currentLayer.property("scale").expression = bounceExp;
	}

	//Main:
	//Makes sure that there is an active comp
	if (curItem === null || !(curItem instanceof CompItem))
	{
		alert ("Please establish a comp as the active item and run the script again.");
	}
	else
	{
		//Loop through layers
		for (var i = 0; i <=(curItem.selectedLayers.length-1); i++)
		{
			//Define the layer in the loop we're currently looking at
			var curLayer = curItem.selectedLayers[i];

			//Check to see if curLayer is a footage layer
			if (curLayer.matchName == "ADBE AV Layer")
			{
				//Add the bounce expression
				addBounce(curLayer);
			}
		}
	}

	//Ends the undo group
	app.endUndoGroup();
}