[exim] Submission mode: change return path without adding Se…

Is it possible to configure submission mode so that the return path of a
message is set to the $authenticated_id, but there is no Sender: header
created?

I'd like to trust my users to set whatever From: address they like, but
still ensure that bounces go to the authenticated sender address. But
the default behaviour of adding a Sender: header mucks up the way some
MUAs (outlook 2003, in particular) render the From: header.

Thanks,
- Marc