route add -net 192.16.5.0 netmask 255.255.255.0 eth0

Of course adjust as you need (eg. the 192.16.5.0 should be changed to the subnet you need access to and eth0 should be changed to the network device that you want that subnet routed through).   I also use the /etc/sysconfig/rc.local script and add the above into it (remember that this route only gets added AFTER all other init scripts have finished though).