Adding IP to Metrics Header

In searching the logfiles for those messages that have hits on rep, I
would like to be able to get an idea of what servers (IPs) are sending
these. Since the dcc checking mailservers are internal (i.e. MX IP
entries in whiteclnt) I cannot use the relay information in the maillog
files.

As such, what would be involved with [optionally] adding IP to the
Metrics header that is added so that it would resemble

X-DCC-brand-Metrics: chost server-ID; bulk chknm1=count ... IP=[relay IP
that is checked by rep]

Just trying to get some useful statistics gathering in one grep/awk pass
of the maillog :-)

Sven