Possible to set Wallpaper (KDE Plasma6) without use of home manager?

Hey all!

I have a setup in which I’m using SSSD to remotely authenticate users. As such, I’m trying to not use home-manager as the users do not exist on the machine before first sign in. I would really like to set a global background for all users on the machine.

I have attempted with the following:

environment.etc."wallpaper.png".source = ../assets/wallpaper.png;
systemd.user.services.set-wallpaper = {
  enable = true;
  wantedBy = [ "default.target" ];
  after = [ "graphical-session.target" ];
  description = "Set wallpaper";
  serviceConfig = {
    Type = "simple";
    ExecStart = ''/run/current-system/sw/bin/plasma-apply-wallpaperimage /etc/wallpaper.png'';
    Restart = "unless-stopped";
  };
};

… but to no avail. Has anyone had in lucky in trying to do this?
All the best & kind regards.

What do the logs for that service say?