docker run -v $OVPN_DATA:/etc/openvpn --log-driver=none --rm kylemanna/openvpn ovpn_genconfig -N -d -e "route-nopull" -e "route <IP OR SUBNET YOU WANT TO ROUTE TO> 255.255.255.0" -u udp://<VPN SERVER>
In client config, add the following line:
route <IP OR SUBNET YOU WANT TO ROUTE TO> 255.255.255.0 vpn_gateway