[users@httpd] Work around for Incorrect ETag on gzip:ed content (issue 39727)?

[Henrich Kraemer <he...@us.ibm.com>]

I am using DEFLATE to dynamically compress xml files using apache 2.0.52
and noticed that etag remains the same whether or not the resources are
send with Content-Encoding:gzip or unencoded.

Issue https://issues.apache.org/bugzilla/show_bug.cgi?id=39727 describes
this issue. I am trying to find a work around by adding some configuration
magic.
I attempted to do this as follows (in .htaccess):

# Set variable UNQUOTED_ETAG to the unquoted etag value if
# this is a resource that will be gzip encoded.
RewriteEngine on
RewriteCond %{HTTP:Accept-Encoding} gzip
RewriteCond %{HTTP:ETag} ^"([^"]*)"$
RewriteRule .*\.(xml)$ - [env=UNQUOTED_ETAG:{%1}]

# If UNQUOTED_ETAG is set modify header to include gzip
Header set ETag "%{UNQUOTED_ETAG}e-gzip" env=UNQUOTED_ETAG

However this is not working. I can observe in the rewrite log:
127.0.0.1 - - [15/Sep/2009:09:35:06 --0700]
[localhost/sid#e35148][rid#1f9e0c8/initial] (4) [perdir C:/Program
Files/Apache Software Foundation/Apache2.2/htdocs/Gzip/] RewriteCond:
input='' pattern='^"([^"]*)".*$' => not-matched

that the input is empty, probably because the ETag is a response header and
not available to the RewriteCond yet.
Is there a way to reference response headers in the rewrite
rules/conditions?
Is there another way to accomplish working around issue 39727?

Thanks,

Henrich

PS:
A later apache version has the Etag header value changed by appending
-gzip. However the quoting wasn't done correctly so that the header in that
version is:
Etag: "44d0ac3fd1f00"-gzip
While the specs require the entire value be in quotes such as in
Etag: "44d0ac3fd1f00-gzip"

Comment 5 of the related issue
(https://issues.apache.org/bugzilla/show_bug.cgi?id=45023#c5) corrects
this:
 <Location /js>
 RequestHeader  edit "If-None-Match" "^(.*)-gzip$" "$1"
 Header  edit "ETag" "^(.*[^g][^z][^i][^p])$" "$1-gzip"
 </Location>
However this depends on the edit feature which is not yet available in
httpd version 2.0.52.