AFAIK you can't with WIndoss builtin stuff. Windows does not monitor login sessions. After a user has logged in, there is no way to tell whether she is still online or not and therefore there is no way to tell if this second login event is a duplicate or not.
I suppose you can do some login script magic and create/check some lock files somewhere that are deleted at logout.. The user is screwed when the clean logout doesn't happen of course.