x11vnc as systemd service steals focus on login screen

[arminfuerst]

I created a systemd service to start x11vnc automatically (tray mode), this is working fine even on the login screen (I'm using lightdm).
There is an annoying side effect: When the service is starting, there is no system tray, so x11vnc starts the icon in a window and this window steals the focus. As x11vnc typically starts while I type the password, this results in a login-failure. I'm looking for a way to start x11vnc in a way that:

• Either there is no icon at all if there is no system tray
• Or the window appears without stealing the focus
  Is there any known way to accomplish this?