So, might it be possible that when you create a map, which includes sprite of a car for example, you still need to have that car sprite in your sprite folder BUT when you host your map first time, the server would "inject" all the sprites and musics to the mapfile, this doesnt include briefing or lua, only sprites and music. And now you just could send your mapfile and briefing to the internet, when all the stuff are packed to the single mapfile.
Now the tricky part, when you open the map in editor again, it shows all the stuff like normal, if you delete sprite, it doesn`t pack up into the mapfile anymore, and if possible there could be option if you want to pack sprites and music to the mapfile or not.
So, that was my suggestion.. hope it will be possible in some build.
-Respect, Monkeyz