Client IP address using Ethernet library

I can get the Ethernet library to serve pages OK, but it would be nice to be able to determine the Client IP address. Since most users will connect through various NAT boxes, the address that the browser sees (eg 192.168.0.27) is obviously not the useful one. There are lots of ideas on the interweb about how to use google, server side PHP, etc, etc, but none that would be much use to an Arduino. Has anyone solved this problem?
I'm sending a bunch of Javascript to format the page actually displayed, so including a bit more to get the research executed at the client end would be one possibility.

Has anyone solved this problem?

Why do you want to? What purpose is served knowing the IP address of the client?

The below might be of use.

Thanks for pointing me at that thread ZoomKat... I searched but did not find it. PaulS: security of course.

PaulS: security of course.

Who's security? Not the client's. There are better ways than knowing the client's IP address.