[exim] Feature req: env var logging

I have a feature request for Exim for consideration, which might be
awkward to integrate.

On an Exim receive (<=) line, the ability to log the value of a
specified environment variable.

Rationale: PHP webhosting, which on Unix uses "sendmail" for submission,
rather than talking SMTP, so the web-server's environment variables will
be visible (by hook or by crook). So if I can log the $REQUEST_URI in
_Exim_'s logs, it should become *much* easier to track down the page
which is being abused by spammers. Sometimes, with large badly-written
PHP applications it can be difficult to tell from the web-server logs
where the hole is.

Please?

Thanks,
-Phil, cleaning up after three customers, on a Sunday.