You could still just use the server.cs to do this properly.
You could send the user's rating, and the user's ip. The data will be sent from the server's ip, but you could just read the user's rating sent with the data.
client.getRawIP()
That's what you need for getting a client's IP.
Actually, you could use the server's ip to tell what server they voted for, and the client's ip to see who is voting.