Remove attachment from SPEmailMessage

I've written an event receiver (SPEmailEventReceiver) which is used to populate metadata based on the email message contents. The event receiver saves the attachments in the same document library as the email message (which works as intended), however, there are still copies of these attachments in the actual email message.

What I would like to do is delete the attachments from the email message once they are saved to the document library as separate files. How can this be achieved programmatically?