Starting user system service from udev rules

I’m trying to run a few modifications whenever I’m plugging an USB Keyboard,
but I can’t seem to start the user service from the udev rules?

Here’s what I’ve got:"setup-keyboard" = {
    enable = true;
    description = "Load my keyboard modifications";
    wantedBy = [ "" ];
    serviceConfig = {
      Type = "forking";
      ExecStart = "${pkgs.bash}/bin/bash ${pkgs.writeScript "" ''


sleep 1;

        # Stop previous xcape processes, otherwise xcape is launched multiple times
        # And buttons get implemented multiple times
        ${pkgs.killall}/bin/killall xcape

        # Load keyboard layout
        ${pkgs.xorg.xkbcomp}/bin/xkbcomp /etc/X11/keymap.xkb $DISPLAY

        # Capslock to control
        ${pkgs.xcape}/bin/xcape -e 'Control_L=Escape'

        # Make space Control L whenn pressed.
        ${pkgs.xorg.xmodmap}/bin/xmodmap -e "keycode 65 = $spare_modifier"
        ${pkgs.xorg.xmodmap}/bin/xmodmap -e "remove mod4 = $spare_modifier"
        ${pkgs.xorg.xmodmap}/bin/xmodmap -e "add Control = $spare_modifier"

        # Map space to an unused keycode (to keep it around for xcape to
        # use).
        ${pkgs.xorg.xmodmap}/bin/xmodmap -e "keycode any = space"

        # Finally use xcape to cause the space bar to generate a space when tapped.
        ${pkgs.xcape}/bin/xcape -e "$spare_modifier=space"

        echo "Keyboard setup done!"

  # SUBSYSTEM=="usb", ACTION=="add", RUN+="${pkgs.systemd}/bin/systemctl --user restart setup-keyboard"
  services.udev.extraRules = ''
        SUBSYSTEM=="usb", ACTION=="add", \

Had the same problem when trying to run actkbd as a regular user to fire pulseaudio-ctl with media keys. You have to write ENV{SYSTEMD_USER_WANTS}+="setup-keyboard.service".