Call the waiter over, point out your paramour and ask him “Could you send that young lady a glass of water with my compliments?”. The waiter duly goes over to her table, places the glass of water in front of her, and says “with the compliments of the young gentleman”. Her eyes widen, she stares at the drink, looks up and searches the room. Her gaze rests on you for a moment and your eyes meet. Raise your own glass of water to her and throw a smouldering look across the room.
This has worked. Twice.