ActionScript 3.0 :: Preloader For External SWF Loaded Via Loader Class

I'm hoping to implement a preloader on a main.swf that measures the bytes etc loaded in an external.swf. My two concerns are that 1) this just isn't possible? 2) I can't have multiple preloaders on the main.swf, which I would if I used one for the external .swf. I intend to try and explain this in the best way I can what I have done so far, as I personally feel this is quite a complex task.

Here's the basics:
I have an external .swf file, being loaded, using the following Action Script (3), in what I shall call, main.swf:

//---loader---
var swfLoader:Loader = new Loader();
addChild(swfLoader);
var swfURL:URLRequest = new URLRequest("nameofswftobeloaded.swf");
swfLoader.load(swfURL);
function loadHandler (event:Event){
var thumbsPanel:MovieClip = event.target.content;
addChild(thumbsPanel);

This works fine. The Action Script I use after this simply allows me to control the external .swf from the main .swf so isn't necessary.. I finish the loader, with this:
"swfLoader.contentLoaderInfo.addEventListener(Event.COMPLETE, loadHandler);"
So, this all works fine. However, as the external .swf contains images, it doesn't load instantly. I therefore need some kind of preloader to show how much of the external .swf is loaded. However, I tried placing this in the external .swf itself and it failed miserably - for some reason it basically didn't preload and the completed phase of the preloader just appeared.