Hi,
to add a static route to a Windows machine use the route command.
Let us assume you have network 172.31.10.0/24 which you can reach over the gateway 10.10.10.200. Your IP is 10.10.10.20 (in same subnet as the gateway).
Use
D:\> route add <destination> MASK <mask> <gateway>
To add the persistent route use
D:\> route -p add 172.31.10.0 MASK 255.255.255.0 10.10.10.200
Optionally you can also specify the interface and the metric (priority).
Michael