Another option would be to install some counter type seating for say 8 coffee drinkers. They would have their own special area. We tell large groups up front, that they can have space for 2 hours when we have other groups in behind them. Communication is key. If your coffee customers are coming in before lunch, you can limit their stay.
Most guests know the difference.
I know that in our establishment that any one desiring just dessert has the foresight to call and ask if that would be okay or inquire politely at the door. I always accomodate. If you can accomodate, as in you are NOT swamped with reservations, I say let them enjoy your view. But let them feel they were an exception to a rule. If so I would not give a thought to explaining that a particular area is reserved for dining.