As per Facebook, this is restricted to apps.
But why not posting to your wall and tagging the friend you want?
Since the newest update has the ability to change the icons and menu bars to the chosen Windows phone color, would it be possible to add this:
leave the app (or at least a part of it) running in the background and check regularly whether the default empty inbox icon changes to the icon showing 1, 2, ... new messages. This once the icon changes, the app can send a notification that one or more messages have arrived in your inbox. No need for the 20min waiting option or other workarounds, ... You could add an option where the user can choose at what intervals the inbox icon should be checked: every 5 min, 10 min, 15min, ...
The notifications (tile or toast or lockscreen) don't even need to be detailed, just a "new message" would be enough.
No Facebook app (not even the official one) is able to do this. JDB Facebook could be clearly the best facebook app without any contest with this feature!
If you cannot use the buttons on Pages or Event pages, please help us report this to Facebook by doing:
Left side menu (///) > "Report a problem"
On the problem description write "Cannot use buttons in Pages or Event pages" or a more detailed report if you want.
This bug is on Facebook side and related to Windows Phone only.
Fixed in FB 1.4.8 and SS 1.2.6
Customer support service by UserEcho