If what you need is to just use the Windows 8 iso to perform a repair, you can burn one on a usb drive also using the official and surprisingly named "Windows 7 usb/dvd download tool", which works just fine also with 8/8.1 isos.
That's what I eventually tried. But the format of the iso was apparently wrong and I rage quit.
Anyways, my optical drive should arrive tomorrow and a friend happens to have exactly the cables I need.