I'm using the master/slave pins on the back of the hard drive in conjunction with a couple DPDT switches to "set" the OS before starting the computer. So each hard drive can be set Master or Slave from the front of the computer BEFORE turning the computer on.
Be sure not to flip the switches while the computer is running... could be a bad thing :D
Step 1: Mounting the switches
Step 2: Building the harness
I removed the "thick" wire from the audio cable because it was not shielded and moved the other wire over (finished product in the second photo). Very patient/delicate work, but worth it. By pressing in on the metal tab that holds the wire in place, the wire will slide out connector and all from the molded plastic. This allows you to change the wires position in the plug.
Using a utility knife I also shaved off the "clips" and alignment pins from the molded plastic connector. They won't fit over the jumper pins otherwise.