ASUS UX31A - A required CD/DVD drive device driver is missing [duplicate]

I have a little issue with my ASUS UX31A. I just tried to do a clean install of Windows 7 64bit using a USB-Stick created using Rufus.

The laptop booted from the USB stick and opened the Windows installation, after a few clicks I got the message "A required CD/DVD drive device driver is missing. If you have a driver floppy disk, CD, DVD, or USB flash drive, please insert it now.".

I have tried literally every suggested trick (putting USB3 drivers on the stick, switching USB ports after error message...) but nothing works.

I have no idea how to proceed and would be happy for any helpful suggestions.

This message happens when you try to install Windows 7 via USB flash drive and use the USB device on a USb 3.0 port. Windows 7 doesn't support USb 3.0 out of the box, so you must inject the USB 3.0 drivers into the Boot.wim with DISM first.

dism /mount-wim /wimfile:boot.wim /index:2 /mountdir:mount

dism /image:mount /add-driver:"usb3" /recurse

dism /unmount-wim /mountdir:mount /commit

Now copy the modified boot.wim to the flash drive.