How to append another stream to ffserver when it is running?

Question

I'm setting up a live streaming WebM video with FFmpeg. The configuration file for ffserver is coded as follow.

Port 8090                      # Port to bind the server to
BindAddress 0.0.0.0
...
<Stream test.webm>              # Output stream URL definition
...
</Stream>

And then start the ffserver using the following code.

 ffserver -f ./ffserver.conf

Since the ffserver is running, How to append another stream without restarting the server?