By following these steps, you should be able to create a Windows 7 USB installation media using the Win7 USB 3.0 Creator v3 tool repackaged by Win7Admin.
# Mount the ISO $mountPoint = (New-Item -ItemType Directory -Path "C:\mount").FullName Mount-DiskImage -ImagePath $isoPath -MountLocation $mountPoint win7usb30creatorv3win7admin repack