When using the windows VPN, the gateway to the corporate network is the same as the assigned VPN/Virtual adapter's IP. This may be static or dynamic. The "use default gateway" option creates a route forcing all traffic to the remote network using that gateway. You can verify this by running route print at a command line. Therefore there is nothing gained by adding a route, and actually you should receive an error to the effect that the route is alresdy in place. If you wish to try, the route statement would look like the following, assuming the VPN client were assigned the IP of 10.0.1.210 (which is also the VPN gateway address)
route add 10.0.1.0 mask 255.255.255.0 10.0.1.210
this will route all 10.0.1.x traffic to the VPN server, however it will not as a rule allow you to connect to other devices on the remote network other than the VPN server.