ActionScript 3.0 :: Copying Multiple Files (within Filesystem), Progress Bar

I'm in the middle of something that's somewhat perplexing. Brief synopsis: It's a full screen kiosk type application with only touch screen control. Sometimes, administrators need to extract large chunks of data onto a USB memory stick to take offsite.

there's a folder on the filesystem with permissions set so that the user that is the web server can access and control it. There are around 100 directories in this folder, each containing around 40 megs of data split into around 10 different files. It's this directory structure I am copying to the USB stick.

Right now, I'm using AS3 to trigger AMFPHP which successfully executes the copy, but it takes about 5 minutes to complete the action, so obviously it needs a progress bar to show state of the copy.

I can execute the linux command of

Code:
exec)("cp -r /$origFileDirectory /$usbStickDirectory");

which obviously works, but there's absolutely no feedback until the entire operation is done (like I said, between 3 to 5 minutes)

Is there anything native to AS3 that I'm missing? Perhaps I've run too far down the PHP path and missed something obvious on the actionscript side?