Add route through specific router(s)
Add split routes for identical subnet schemes
Use for when you have two routers on LAN that happen to have a similar subnet scheme, or if you have an identical LAN subnet scheme as the device on the VPN connection.
route add 192.168.1.0 mask 255.255.255.0 10.100.98.25 route add 192.168.0.0 mask 255.255.255.0 10.100.98.87
Note: The exact command may differ for your operating system, but there is a synonymous command for any networked operating system; as they all use route tables.
Taken from my response in ServerFault