Download MP3 instead of open in WMP or browser?

Hello - here's the simple code I'm working with:

download_btn.addEventListener(MouseEvent.CLICK, onDownload);
function onDownload(e:MouseEvent):void {
    var dl_request:URLRequest = new URLRequest(current_url);
    try {
      navigateToURL(dl_request, '_blank');
    } catch (e:Error) {
      trace("Error occurred!");
    }
}

Basically, this is a button that (when clicked) is supposed to allow the user to download an MP3 file.  It works as planned except that when the button is clicked, the MP3 just opens up in the browser or in Windows Media Player or whatever default "playing" application the user has.  I want it to work in the same way as when you right-click a link and choose "Save Link As..." so that when they click it they actually will save the MP3 file itself to their computer (so, the "Save" dialog box will pop up when they click the link), instead of the file just opening/playing.

Is this possible without making separate .zip file versions of all the MP3s?  Thanks!