Multi hop routing

As far as I can see, this is not possible without changing Openvpn Server configuration.
I have implemented similar scenarios with certificate based authentication, and it is working. I am assuming this is a road-warriro setup and not a site-to-site connection. Which means, the VPN Server is only aware of a single client and not of other machines trying to connect over the same client. From a security perspective this also makes sense for me.
Now if more machines need to connect over the client computer, it will then act as a gateway, and this can be configured at the Openvpn server. Details instructions on setting this up can be found here:

Expanding the scope of the VPN to include additional machines on either the client or server subnet.

See: Including multiple machines on the client side when using a routed VPN (dev tun)