No problem:
- Get a copy of nixpkgs:
git clone https://github.com/NixOS/nixpkgs - Save the snippet to
iso-image.nix - Adapt the first line of the script that it points to location of
nixpkgs(from step 1) - run
nix-build iso-image.nixto build the image. - In the folder
result/you will find the iso-image, which can write to a USB stick withdd