No... They wouldn't. Not sure where you're getting the 5 work station thing per license, but the whole backup idea is getting into something you might call a loophole. First off, it's not a viable install, in that you couldn't just pop it into any random computer and boot it, you have to restore an image of some sort. Even if you had some program that created a viable and bootable backup, that would be a violation of the EULA, but it gets back to Hollywood's attempts to get the VCR banned, which rather backfired on them when the Supreme Court ruled that the VCR's recording function could be used for non-infringing purposes, thus could not be banned. It would be a violation of the EULA for you to use it for that purpose with Windows, but because you could, for example, potentially use the same software to create backups of Linux or FreeBSD installs, both of which do not place any restrictions on the number of computers you can install the software on, it would have non-infringing uses and thus it's how the individual chooses to use the software.
It's really very simple, no matter how complex you want to try and make it. The EULA for Windows prohibits multiple installations on any given computer barring things like multiple licenses and volume licenses. End of story, do not pass go, period, the end, finale, etc, etc. You have to agree to said EULA before you are allowed to even install Windows, so you're basically screwed by the time it gets to court.
Personally, I think it would be interesting to see what would happen if someone were to take the Windows install disc, make their own image of it (perfectly legal under copyright law to make a backup copy of install media) then edit the text file that contains the EULA text and is read in by the installer. If someone were to modify that EULA to read as giving them the ability to do pretty much whatever they please with the software, I would not be at all surprised if they won. Courts have been rather dubious of click-wrap licenses as it is and if the company chooses to basically assign power of attorney to a piece of software like that, they'd probably have a hard time finding a viable legal argument to challenge it with. It'd be even worse than the "robo-signers" that the banks got into big trouble with, because at least in those cases there was an actual person signing the documents, even if they didn't do the due diligence required. In the case of companies like Microsoft, Oracle, Apple, Google... They rely entirely on a piece of software to register that you agreed to something. And one of the lesser known facts about contract law, is that until both parties sign, you're free to modify it any which way you want. You can strike out parts of it, add in other parts, and if both parties sign the document indicating they read and agreed to the terms, it's binding. So again, if all these large software companies are giving power of attorney to a piece of software, which is based on the assumption that people will not modify the contract before agreeing to it, that's their problem. You could even go after them by saying they're intentionally trying to deprive you of your legal rights to modify the terms of the agreement.
As soon as the first person did that, you'd see the software industry move faster than you've ever seen it move before. It'd be interesting to see what they came up with. The obvious first move would be to try and just stuff the text of the EULA into the binary blob of the setup program, but that wouldn't address the legal right of you and me to modify those terms, so that probably would not put them in the good graces of the Court. It'd be interesting to see what the companies did ultimately come up with. Microsoft might just try and pout and say they won't activate the software, but you could write into the EULA that you are free to install software that removes or disables that particular functionality and also give yourself the same retroactive powers companies write into EULAs for themselves, so that you can modify the terms of the agreement at any time and submit it to some address at Microsoft and if they do not respond within X number of days, it is assumed that they agree.
I would gets me some popcorn to watch that particular bit of legal drama play out.