AS3 - dynamic class names with *new* operator?

I’m using ActionScript 3 and Adobe Flash 9 Public Alpha.

I have 50 movie clips in the Library that use Linkage to set the Class name to: Img1, Img2, Img3, …, Img50.
I have a parent class named RandImg. I want the constructor for RandImg to randomly select one of the 50 movie clips from the Library and display it. I could get this working by generating a random number, and then writing a really huge switch statement to associate each possible random number with its respective Library Movie Clip Class name, but I would much rather do this with a dynamic/variable class name based on the random number, such as:

var nImgChoice:Number = Math.floor( Math.random( ) * 50 ) + 1;
var mcImg:MovieClip = new [ “Img”+String(nImgChoice) ] ( );
addChild( mcImg );

Note that this used to be possible in AS 2 by doing the following:

this.attachMovie( “Img”+String(nImgChoice) , “mcImg”, this.getNextHighestDepth());