[Exim] Rewriting subject header.

Hi all,

I'm using Exiscan, and it allows me to add an additional Subject header
prefixed with "SPAM" (or some variation). Since it adds the header, some
MTA's get confused and display the first Subject header, without the SPAM
tag. I would prefer to rewrite the subject header entirely. How can I do
this? I recall a thread about using a script, but I haven't been able to
find it in the archives.

Thanks,

-- Steve