In the project.xml, something like,
<assets path="sounds" embed="false" />
That should prevent loading them as part of the preloader. Then, later, you should be able to load on your own:
Assets.loadSound ("sounds/sound1.ogg").onComplete (function (sound) { ... });
When you do this, we should keep it in cache, so you may have to either set caching to false in loadSound or go to Assets.cache to remove the sound when you are done with it.
It might also be necessary to call sound.close () to get our HTML5 sound library to dump the loaded sound