I would rig it as a stage aswell.
- You can turn the tank valve off and on easily. (Hose presurised, tank off)
- You can dich it.
- You can hand it off.
- The reg can be nicely secured.
- Its adaptable to more advanced diveing.
- Its extrodinatly easy to manipulate.
- Its easily identifiable to a complete stranger.
"Ok, buddy... the yellow one is my octo, and the green one is my pony". Try that at 60 feet in dark water while your out of air, not that it truly matters which you grab.. its still an extra step.
All said, your likely better off diveing doubles with an isolated manafold if your looking for more redundancy than your buddy.