I gave up setting the gateway in the openvpn config.
i added a up script to the openvpn server.
#!/bin/sh
ip route add 10.8.0.0/24 dev tun0 table 12
ip route add default via <my vpn client> dev eth0 table 12
ip rule add from 10.8.0.0/24 table 12
ip rule add to 10.8.0.0/24 table 12