No different than rolling your own WinPE or using the latest build of MDT to deploy Win7. I actually had no idea that you could do that! I have had my slipstreamed Windows 7 ISO for so long that I haven't looked into that in forever. You can just use Win10 media and replace install.wim with an install.wim from Win7 media to get around driver issues.
Try this tutorial if you absolutely need to use Windows 7. The Windows 7 installer doesn't natively support USB 3.0 so it will give you a hard time unless you create the installer with USB drivers slipstreamed into it. Ahora vas a la pestaa Boot, en la opcin Boot Mode cambias UEFI por Legacy Support. Otherwise, you may struggle using the Windows 7 USB installer if you only have USB 3.0 ports. Instalar Windows 7 / 10 Lenovo G50 En el Lenovo Button Menu escoger la opcin BIOS setup, pestaa security y dejas Secure Boot en disabled. If so, the PC will reboot and use Windows 10 Pro afterwards.
Have you tried just using the Windows 7 Pro key to update to Windows 10 Pro? Is there a reason you want to revert to Windows 7 (other than the obvious Windows 10 semi annual update disaster)? You might be able to just change the product key with the one your boss gave you.
