I achieve mostly the same on a non nix-darwin setup using vanilla home-manager:

  home.file."Brewfile" = {
    onChange = ''
      HOMEBREW_NO_AUTO_UPDATE=1 /usr/local/bin/brew bundle --file="$HOME/Brewfile" --cleanup --no-upgrade
    '';

    text = ''
      cask '1password'
      ...
    '';
  }