[exim] Expiring (removing) old mail and updating maildirsize

I've searched and searched but can not seem to find an answer.

How does one gracefully remove user e-mail older than a set period, and at
the same time reconcile this with the information stored in maildirsize
quota files?

I need (cough) to enforce an "if it's older than sixty days, we're deleting
it" policy.

But I don't see how to delete old mail, and at the same time update the
maildirsize file in the users maildir such that the deletion is reflected in
their quota.

So far the best I can come up with is make a list of users with mail over
sixty days old, remove it, then delete the maildirsize file from each one of
those directories and let Exim handle rebuilding it.

Steve