[Exim] Removing Read Receipt Requests on the fly

All,

Has anyone got a neat way of mangling mail headers in Exim-3 (or Exim-4
if I were to upgrade) for in-bound mail to remove the headers that control
read receipts:

    Disposition-Notification-To: "Foo Bar" <foo@???>

perhaps changing it and defang-ing it to something like:

    X-Removed-Disposition-Notification-To: "Foo Bar" <foo@???>

Mike