Situation: I have some Windows 7, 8, 8.1 machines eligible for upgrade but various issues prevent me taking advantage of the free offer right now. Translation: I waited until the last minute as usual. Premise for solution: if Windows 10 has ever booted on a machine and activated with a digital entitlement, that same entitlement will be retained for future activations. It\’s activated for life per Microsoft\’s original announcement. Solution:1. get a USB attached hard drive or SSD.2. install a product called WintoUSB Free – Best Windows To Go Creator to create bootable Windows 10/8.1/8/7 USB drive!3. Use it to create a portable version of Win10 from the appropriate ISO of 1511/10586 (home or pro to match the installed OS on your machines) on the USB drive. Do the next steps on each machine:4. Plug in the drive and boot from it.5. Go to settings, update/security, activation.6. If it doesn\’t automatically activate, enter the product key found on the sticker or with your retail 7, 8, 8.1 package.7. This should give you a Digital Entitlement.8. Shutdown and disconnect the USB drive.9. Turn the machine back on. It should boot normally to the original OS. Congratulations, you have registered your "upgrade" on Microsoft\’s HWID servers and can install Windows 10 for free on that machine whenever you are ready. I tested this process on the four machines at my office which have weird hardware dongles or line-of-business software which we don\’t know yet if it\’s compatible. Everyone else got an upgrade this week or earlier. I hope this may help someone during the 20 or so hours that are left.