you need to make calljs load external js file which contains all your media:
var sound1 = new Media(src);
var sound2 = new Media(src);
... so on.
this has some problems though, tested in on start of first layout, and for some reason calling just sound1.play() didn't work, but calling alert('play sound');sound1.play() worked.
also this should really be implemented somehow automatically by construct export hopefully in some of the next releases right?