Brian, I think this will be solved soon, as developers and users familiarize themselves with Android 4.2. Right now, your original music is stored in mnt/shell/emulated/0/music, and your new account looks for its music in mnt/shell/emulated/1/music. Each user only sees sdcard/music, with his account following its individual path to his music.
I'm sure it will be easy for someone to develop a way for users to access a shared directory or directories, and rooted devices can do it already. Of course, rooting also unfortunately takes away the privacy of having individual accounts.