securing webservice stream using encryptbody policy

I fail to find any example of attempting to secure a webservice communication with the' encryptbody' policy using a symmetric key.
In fact,all examples tend to attempt all securing activities(signing,securing,encrypting et al) with the use of certificates.
We have a used-case wherein the partners are known and need to encrypt the communication using a known symmetric key.
We have our own authentication module - the only aspect of concern is encrypting the stream ,preferably using a WS-Policy,rather than writing our own handlers.
Any help on this will be greatly appreciated.

When you asked this question before, I pointed you to an article that explains how to do this using Axis; didn't that work out?

can you please point me to the first part of that write-up too.
It seems there is no easy link to the first part which seems to talk about authentication.