Check out Chapter 17 from Core Servlets and JavaServer Pages by Marty Hall (It's available online). Section 17.3 discusses "Sending Data with GET and Processing the Results Directly (HTTP Tunneling)" Hope that Helps!
I've done this before. I set up HTTP tunnelling for my last project. Use the O'Reilly book 'Java Servlet Programming' by Jason Hunter Chapter 10 - 'Applet-Servlet Communication' as a reference. It was a good reference with code examples of server and client.
Using our HTTP tunneling solution, applications can move requests and data through a Port 80 restricted firewall to and back from external Application Servers as easily as they can with no firewall in place. Nothing in the firewall setup needs to be changed and no involvement is required from firewall administrators and/or IT personnel. I hope this will help. ss