http://stats.i2p:81/ has some howto links

For HTTP virtual hosts on the same web server, all you have to do is set hidden services custom option spoofedHost.xxx=vhostname.i2p where xxx is the i2p port.

To route to a different web server (or for standard servers), the custom option is targetForPort.xxx=localhost:localport

examples;

spoofedHost.81=port81.i2p
targetForPort.81=localhost:7777