It automatically injected the necessary USB 3.0 (xHCI) drivers into a Windows 7 installation image.
If you locate a mirror of the original Intel utility (use caution and verify file hashes), the general process is: It automatically injected the necessary USB 3
How to Interject USB 3.0 Driver onto Windows 7 Bootable USB? It automatically injected the necessary USB 3
Once completed, safely eject the USB drive. You now have a fully functional Windows 7 USB installer with USB 3.0 support. It automatically injected the necessary USB 3