Hi Rojopipe,
If the appliance has already been initially setup with bootstrap, then the easiest method is to use the "routeconfig" command to create your desired static routes.
In the example below I'm showing the routeconfig help info (routeconfig -h) then issue the routeconfig command and create a static route for the class C network 192.168.168.0/255.255.255.0 to be routed via 10.0.4.66. I then add other route for a different class C network using CIDR notation (192.168.169.0/24)
The routeconfig command can be run again, and will give options to update, delete, or skip any of your existing static routes as show below where I remove the routes I created earlier