Once again, kju will probably want to prove me wrong, but unless they've fixed this for A2, the answer to this is: you can't. It works in addon configs, but it doesn't work in the mission description.ext, even though the two look identical. I wish it did, but it doesn't.
The one who provides a working example mission that, only through adding it in the description.ext, is capable of refering to a sound that resides in one of BIS's pbos and making it work, will get a big ol' Wolfrug-cookie. No, not a "theorethically it would work like this", but tested and working please.
note: some sounds might actually have definitions in a cfgsounds someplace, which would make them show up in for instance a trigger's Effects/Anonymous sounds menu.