How to clean install Windows 8 Pro *Upgrade* on BootCamp already running Windows 7? Now that Windows 8 is officially supported in the latest BootCamp, I am considering this for my Mac.

There is plenty of general advice about installing Windows 8 / Windows 8 Pro in BootCamp on a Mac.

However, what I do not see is how to clean install a Windows 8 Pro upgrade on a mac with an existing BootCamp Windows 7 install. Clean install is an option offered in the upgrade install process for general PCs - but can this work on BootCamp?

Why do I want to install Windows 8 Pro upgrade ?

Because it's much cheaper than the regular version (though it is still a full OS install) and I am eligible in that I already have a legal licensed copy of one of the pre-requisite operating systems to qualify - I have Windows 7 64bit installed in bootcamp on my mac. In other words Microsoft offer Windows 8 cheaper if you have a legal copy of an earlier qualifying OS.

What do I mean by Windows 8 Pro clean install?

I also have a desktop PC which used to run Windows 7. I clean installed the Windows 8 Pro upgrade on this successfully. Although Windows 8 Pro upgrade is a full OS installation, during the install process, it will check the hard disk for the presence of a valid, licensed eligible OS already installed - in my case Windows 7. BUT, once its done that, it offers the option to format the disk on which it is to be installed. Obviously I would have backed up any valuable files, deactivated any applications and uninstalled them -ready to reinstall and reactivate them on the new OS later.  A fresh start. I prefer the clean install approach as to me this is the optimal deployment; no baggage/kruft/residue/ditritus/call it what you will from a prior OS. I also hear anecdotally from friends that an "in-place" upgrade whereby Windows 8 retains personal files and apps during install has proved unreliable for them.

So can anyone advise me about clean installing Windows 8 Pro upgrade on Bootcamp that already had Windows 7 installed?

(By the way, I would not want comments or discussion about why I should have Windows/Windows 8 on my Mac. Not useful to me. I work in computing and prefer to keep a balanced informed opinion of what is out there to help me and others. Thanks!)
It should be possible to do the clean install of a Windows 8 Pro upgrade on an existing installation of an earlier qualifying OS as these steps for Windows 7 suggest:

http://www.tuaw.com/2009/11/02/an-illustrated-guide-to-boot-camp-and-windows-7/

In this guide above, search for string: "Theoretically, you're doing a fresh installation of Windows 7. In that case, select the "Custom (advanced)" installation" 

(remove just the outermost quotes when searching for the string in the guide.)

In summary, after the Mac BootCamp app has done its original setup (including the partitioning), the rest of the setup is as per usual Windows installation - all the Windows steps are shown. In the event of the usual ReBoots, be sure to select the Windows drive to continue the installation.

During the install, once the Windows 8 upgrade installer has found the previous qualifying OS on the disc, it can then offer the format disc as the clean installation option.