[exim] Delay warning to $h_disposition-notification-to:

Is it possible to point delay_warning
messages to an arbitrary address?

I mean something like this:

delay_warning_to = ${if \
                        {def:h_disposition-notification-to:} \
            {$h_disposition-notification-to:} \
            {$sender_address} \
                    }

Please advise.

Everton