I downloaded the Debian amd64 netinstall ISO and put it onto a USB stick. The installer runs fine, but my laptop requires proprietary wireless drivers (iwlwifi) to get internet during the install. During the "Detect Network Hardware" stage the installer asks me for removable media with the drivers on it.
The install USB isn't writable (because it was created using dd and an ISO image). I tried placing the iwlwifi files on a separate USB, but the Debian installer couldn't find/detect them (and unfortunately, the installer doesn't give any info on why it failed - it just pauses for a moment and then goes back to the screen asking for removable media with the drivers on them).
How do I make a USB disk with the iwlwifi drivers that the installer can recognize, or put them onto the installer disk?