Please provide appropriate links to follow if the question is already posted. I searched thru the entire forum but could not find relevant information.
here is the base thing about ipc :
for what you want to do, I guess you'll have to manage something out of the JSR-168 ...
may be with IPC by message (like in the library proposed on this site), you can have what you want.
the only trouble is that the portlet will make the changes in the render phase.
(the action phase is always one and only one portlet involved).
hope this helps...