How can I add permanent static ip routes to Rasplex?

Hi,

I’d like to add two static routes to the routing table of my Plex Client (Rasplex).

Neither of the known solutions work:

  1. There is no option to add static routes via the GUI (network settings menu). Maybe I haven’t found it?
  2. I can’t find the local network configuration files for each interface on the client to add the routes manually. Those, I’ve found are empty.
  3. I also cannot add the “route add …” command to a /etc/fstab file which doesn’t exit.

What is best practice to add static routes permanently to the Rasplex client?