Sorry my post is not a detailed as I would normally have been. Kinda busy at the moment. I think you get the idea.

It does accomplish the "instant switch" you are looking for.

Since the "other applications" were not mentioned, my assumption is that you are not as concerned about continued functionality of those apps. during the upgrade.

If you don't have an old server laying around you could take a desktop pc or even a laptop and throw a spare drive in it that you can format to get the temp server running. Then when done just swap the drive back in the desktop or laptop and you are right back to where you were before.