Here is the original link supporting the OpenVPN 2.x client-to-client feature:
Uncomment this directive to allow different
clients to be able to "see" each other.
By default, clients will only see the server.
To force clients to only see the server, you
will also need to appropriately firewall the
server's TUN/TAP interface.
Uncomment out the above client-to-client directive if you would like connecting clients to be able to reach each other over the VPN. By default, clients will only be able to reach the server.
Next, ask yourself if you would like to allow network traffic between client2's subnet (192.168.4.0/24) and other clients of the OpenVPN server. If so, add the following to the server config file.
push "route 192.168.4.0 255.255.255.0"
This will cause the OpenVPN server to advertise client2's subnet to the other connecting clients.