[Exim] Rewriting subject.

Hi all,

I recently installed Exim 4.30 with the Exiscan patch. The recommended way
to add a "spam" tag to a subject header according to the Exiscan docs is
below, but I find it only ADDS an additional subject header. I've looked
through the archives, and apparently this is well-known Exim behavior. Is
there an alternative way (than the one below) to REPLACE the subject line
with a new one (that simply appends a spam tag to the old one), preferably
working with an ACL (such as the one I use for Exiscan)?

Here's what I use now:

warn message       = Subject: **SPAM** $h_subject
         spam            = nobody

Thanks,

-- Steve