[exim] Adding informative headers to bounce messages

I'm trying to work out how to add useful headers to the bounce
messages that Exim generates in order to assist automatic processing
of error messages. I've googled quite a bit, and read through the
Exim book, but can't find anything on it.

Any information on how to add more information such as the error
message or error code to the headers, would be greatly appreciated.
Even if people can suggest terms to search for, that would be good.

Thanks

Ed