Although I have
yet to try this, I don't doubt that it will work, however I'm not quite sure it is worth while since, as it even mentions, performing a clean install is always best as well it takes a lot less time. As well, the time I save can go towards reinstalling the various programs that would have had to be installed again anyway, should you choose to use the update.
The real work around would be purchasing the Windows 7 Disc and then simply insert the disk and allow it to update the key by agreeing to the license and entering the certification key but this is just not going to be an option unfortunately.