[Exim] autoreply with changed sender

I'd like to use "mail" command in Exim filter and change the default
sender for this bouce message. I can't use empty '<>' sender in one case.
I think "pipe" command wouldn't be the best method because bounced message
doesn't contain any element of original mail. What can I do?

-- 
Piotr Roszatycki, Netia Telekom S.A.                    .''`.
mailto:Piotr_Roszatycki@netia.net.pl                   : :' :
mailto:dexter@debian.org                               `. `'
                                                         `-