Feature request: "While away message" for PM

It would be very nice if users could activate some sort of "While you're away" feature for users sending them PMs while they are away.  That way users could update their profile and indicate to other users that they are not available.
 
If we cannot add that functionality through automated email/PM replies it could be in the form of a statement on the user's profile when viewing his profile or the user list.
 
Because I have the admin account, every time a user is away and a PM is sent to him, the auto email reply is being sent to the account used to send the PM notifications but the originating user never gets that "absence" notification.
 
Any ideas?