I can't think of any way to remotely implement an archival procedure. I think you'll have to wait until those managers come into the office and catch them then.
What we do is to enforce a max mailbox size on the server of 50MB storage and we don't archive ON the server. They must move the email off of the server to their local PST files. If they don't and it fills up, they first can not send and eventually can not receive. Instructions went out to everyone on how to keep their email moved down from the server to their local computer. If they don't follow those instructions, they fill up their mailboxes and can't work at all, forcing them to call us for help.
Now, that doesn't force them to archive their local PST files. But, when they eventually call for help because they can't send email, one of the first things I have them do is to set the archive procedure and run it BEFORE I help them get their send capabilities back. Then, I tell them that if they don't allow the local archival procedure to run and keep the PST file down to a workable size, they'll loose everything when Outlook eventually won't open it. :D
One thing you might remember too when setting your policy. Using Exchange gives people easy access to their email while traveling or away from their main computer. If you move too much off of the server so they don't have access unless sitting in front of their own computer, you defeat the purpose of having an Exchange server to begin with.