I think you all are really over-thinking this...
I found the absolute best and easiest way is by using symlinks. This can be accomplished with ROM Toolbox [Root Browser], without the need of scripting/commands/etc.
0. Open ROM Toolbox > Root Browser
1. Make a folder in your desired location (sdcard) called "Music" or something to that sort.
2. Tap and hold, select the option "Create Shortcut" at the bottom
3. Navigate to /data/data/com.google.android.music/
4. Paste (to create the shortcut)
5. Delete the "cache" folder in this directory
6. Rename the shortcut to "cache"