Hello @JoelKelley
Unfortunately we do not support configuration of static routes on the GX at this time. That would be considered a feature request.
To flip this and make it work, point your clients to that raspberry pi as a default gateway (being sure the pi can do IP forwarding), and let the PI punt non VPN traffic to the GX for routing instead. VPN traffic should hit the PI for processing, encapsulation, and forwarding on the VPN tunnel and otherwise hit the PI's default route of the GX for any non VPN traffic (if you are going to use a split tunnel).