IP spoofer problem

Hi all,

I've got a website coded in PHP, and a malicious person is
posting fake spam messages to a low-security forum that I've coded.
My forum code simply reads the POST data and in good faith
posts the message to the forum and records the IP of the poster.
Here is what is happening. Bogus messages are being posted
always of roughly the same type or message, often with
bogus URLs in them, and the IP address that I am recording
is always random i.e. spoofed.

What I would like to do is to have the web server keep the
connection open long enough to ascertain that the real
IP of the spoofer is, or at least to ascertain that the HTTP
request is more than one packet. Is it possible to do either
of these from PHP?

Thanks.