I hate to say it but the only Reliable method I've found to insert the USB 3 and NVME drivers into a Win7 Installer was the Gigabyte USB Patch Tool -https://download.gigabyte.com/FileList/Utility/mb_utility_windowsimagetool_B18.0213.1.zip
Doesn't take too long if the system is fully up and running. You may need a Valid WIn7 ISO to place it onto a flash drive unless you have the free USB DVD tool from MS and a Valid WIn7 Install disk.
I've tried many times and only had one copy work correctly, then promptly lost the updated image - Go Figure. Since the Gigabyte tool has worked reliably, I gave up trying to do more.