Currently not possible with Plus! and i don't think there is any other plugin that does that either. You could just leave the person who is away a message like "hey, give me a sign when you get back".
quote:
Originally posted by rudefrog
At the moment i know it can prompt you in the taskbar
Plus! can pop up a notification indeed. You can also set it to play a sound together with the notification so it draws more attention. See
How do I set a Popup Notification only for a few people?