HTTP pragma-extended

I am looking for a way to rewrite http messages to contain information
not usually available. In reading the RFC on http the only thing that
looks like it might serve my purpose is pragma:

Pragma = "Pragma" ":" 1#pragma-directive
pragma-directive = "no-cache" | extension-pragma
extension-pragma = token [ "=" ( token | quoted-string ) ]

The RFC then goes on to explain how the no-cache must behave when being
passed through proxy. By this then I gather that I can just create a
new token and put what I want in the quoted string after it. Is this
accurate? Is there a more appropriate place to put specialized
information than in the pragma directive? I suppose what I am doing
sort of qualifies as pragma since it is the httpd server on the other
side that will extract that information and use it in a php script...