What you quoted from the OpenVPN documentation is valid only if you use TAP interfaces in bridge mode. In your case, you must not bridge the VPN interface with an ethernet one. Instead, you have to assign the IP address to both the VPN interfaces and then just add the static routes to route your subnets across the VPN. You could also enable RIP v2 so the routing is automatically managed without adding static routes.
This is exactly the same steps you need if you use TUN interfaces.