Turns out you don't actually need an internal drive to run Windows properly.

Can’t boot Windows using a USB drive? If yes, you have come to the correct page. In this post, we will help you find a working fix for boot issues with USB. To boot Windows using USB, you first need ...

When I went into the boot menu after connecting it, I vaguely noted that it only showed the USB drive, but didn't think too much of it. With this drive I got stuck on an empty ReFind screen, so, power ...