@ahlfs I have actually already started to work (still wip) in a theme for kodi just to allow such user preferences. I‘m slowly working on it, so if you have some patience, you‘ll just need to follow easy instructions and everything will work the way you want.
If you are in a hurry, just check for the logs to see how kodi‘s launch command look like and try to adapt it to a working es_system.cfg entry.