How Do I Install NS on Standby Hard Disk without using additonal license

I just installed Norton Security (for 5 Devices) on my WIN7 computer’s active first hard disk. I have a second, standby, hard disk physically mounted in my computer, but it is not connected. The second disk is essentially a clone of the active first hard disk that has an expired Norton Antivirus installed.
Should the currently active first hard disk fail or pick up a nasty virus (I don’t trust a virus cleanup), I will disconnect it, then connect and run on the second, standby, hard disk.

MY QUESTION:
I wish to temporarily run on the second hard disk in order to install Norton Security on it, then disconnect it to go back and run on the first hard disk.
How do I install Norton Security on the second hard disk and avoid using up one of my available device licenses?
(Imaging the first to the second hard disk is one solution, but I prefer not to do this because the Windows registry on the second, standby, hard disk is much cleaner than the first)

NOTE: Since I will NEVER run more than one instance of Norton Security on my computer, I do not believe the above process violates the license agreement