Manually manipulate the routing tables. Requires root privileges. More information: https://keith.github.io/xcode-man-pages/route.8.html.
sudo route add "destination_ip_address" "gateway_address"
sudo route add "subnet_ip_address/24" "gateway_address"
sudo route -t add "destination_ip_address/24" "gateway_address"
sudo route flush
sudo route delete "destination_ip_address/24"
sudo route get "destination"