Você pode executar comandos da configuração openvpn como:
script-security 2
up /path/to/routing/script
down /path/to/routing/downscript
do man openvpn:
--up cmd Run command cmd after successful TUN/TAP device open (pre --user UID change). cmd consists of a path to script (or executable program), op‐ tionally followed by arguments. The path and arguments may be single- or double-quoted and/or escaped using a backslash, and should be separated by one or more spaces. The up command is useful for specifying route commands which route IP traffic destined for private subnets which exist at the other end of the VPN connection into the tunnel. For --dev tun execute as: cmd tun_dev tun_mtu link_mtu ifconfig_local_ip ifconfig_re‐ mote_ip [ init | restart ]