[Exim] stupid question

This isn't really exim-specific. Suppose a batch of mail is delivered
to a file. Now you want to requeue it for delivery elsewhere. For
example, suppose someone left the company, and now you want to forward
all his mail - but he already has mail in /var/mail/user. What's an
easy way to do this? That is - so he receives the mail as individual
messages - not as one big mail.