Waiting outside their office
It takes a certain kind of self confidence to hover outside of someone's office while they are on the phone, or face to face, finishing up a conversation.
If the most important thing for you to do is to get an answer from this person, or make sure this person is aware of something - then just wait. It's not wasted time; if you move on to do something else, no telling when you'll get back to this issue.
Also - you're making an interesting statement to the person you are waiting on; that they are worth your time to wait for them to fininsh what they are doing, and also that this issue is important enough for you to wait.
The hovering thing also makes people finish with the small talk a bit quicker. Of course, it's always good form to apologize for the hovering - but then, get to the point of your questions / FYI session quickly.