How to activate Windows 10 Pro without installing previous version first?

Here's the situation: I own Windows 7 Ultimate, box version, with product key and all. But I DON'T HAVE IT INSTALLED.

I used my only system SSD to test Windows 10 Insider Preview.

I admit I used pirate KMS to activate it, since it refused to activate.

Now I installed official Windows 10 Pro, but it obviously doesn't activate. At least legally, because activating via pirate KMS still works, but it's not what I need. I'm entitled to free upgrade as legal, registered Windows 7 owner.

I've read I have to wipe my HD, install Windows 7, activate it, install ALL updates (which would take all day), then upgrade (and it would activate then).

Since I don't have whole day to waste for it - is there a shortcut? I'm looking for a way to use my Windows 7 product key to activate my Windows 10 upgrade. I'm positive it's possible, but it requires some magic. Any clues?

Here's my guess, when you do normal upgrade procedure you get new product key for Windows 10 based on the product key you had for previous Windows version. The old key has to be validated first. My question is: how to achieve it using only existing Windows 10 installation? Maybe I could install Windows 7 on virtual machine, activate it and somehow get the new product key from VM? Anyone tried that?

Answer

The Windows 10 upgrade stores your machine ID on Microsofts servers. This means that if you decide to do a clean install at a later point in time, you do not have to type in any product key and that you can just skip it during installation. After installing it will then activate itself (This may take a while.. Took a few hours and some restarts for me).

I actually decided to test this yesterday when installing, so when I was finished upgrading to Windows 10 I extracted the new product key from my registry and then I tried to do a clean install using that key. Sadly the Windows 10 installer doesn't recognize that key as valid.

In short: It doesn't look like there's any "magic" way to circumvent the upgrade method on the first install, since you need to get your machine ID up on Microsofts servers to be able to activate your Windows 10 installation.

Are you sure you need to get all the updates for Windows 7 first? On my laptop I was able to upgrade to Windows 10 directly on top of a fresh Windows 8 install.

Update:
You could try to contact Microsofts support. Apparently a few people have had success getting them to upgrade your existing key to a Windows 10 key - Haven't tried it myself though so I can't confirm it.