[Zope] unbuffered response.write through Apache 2.0 reverse proxy?

[Christoph Berendes]

To prevent browser timeout during a long running process, I've got the 
following code to work nicely,when the browser accesses Zope directly 
(e.g. http://myzope.net:8080/folder/client001/)

context.REQUEST.response.write("progressing...")
#do some stuff
context.REQUEST.response.write("further...")
#do some more stuff
context.REQUEST.response.write("done!")


However, when browser goes through the Apache reverse proxy, e.g.

<VirtualHost *:80>
 ServerAlias   site1.foobar.com
....
   RewriteRule ^/(.*) \
      
http://localhost:8080/VirtualHostBase/http/%{SERVER_NAME}:80/%1/site001/VirtualHostRoot/$1 
[L,P]

I get all three writes (progressing..further...done!) at once, at the 
end of the processing.

I'm running Apache 2.0, Zope. 2.7.6, Plone 2.0.5 on Linux
 From going through Apache docs and discussions (notably 
http://www.gossamer-threads.com/lists/apache/dev/305433), it appears 
that this is an Apache 2.0 problem.

Is there any way to get the same behavior (unbuffered writes) even when 
I go through the Apache reverse proxy?