Default [Q] Utilize excess ROM free space via symlink or the likes?

Hey...just wondering. Most custom roms leave us with a whopping 2+ gigs of space free on the system partition.

Is there any method like symlink or folder mount, which could allow us to store, say, mp3s etc. in a folder on the system partition and then sym link it so that apps and the phone thinks they're on the SD card?

Just an is a bit of a shame that we're left with 2 gigs of free space which can't really be utilized in it's present form. there a music player app that would be able to play files stored on the system partition? (assuming, say, that I activated RW on the system, copied in a few folders of music, and then used an app to play back said music now stored in the 2+ gigs of free space on the system partition)?