It's been a while, so I thought I'd bump this back up to see if anyone has any other ideas. I'm hoping to give Moderators a button on each user to allow them to "Follow" the user and get alerts/emails when that user posts something.
The link above is a step in the right direction, but would require an admin to enter the userids, and then the email is sent only to one address. I'd rather have each Mod able to Follow/Unfollow particular users at their own discretion. Thanks!