If you know anyone in real life that is also into lucid dreaming, have you ever thought about setting up a scenario to make him think he is dreaming? It would be hard to do, but the outcome would most likely be hilarious.

You somehow rig the digital watches in the room to change to a different time when you remotely press a button in your pocket (for example). So he does a reality check, he turns his head, you press the button in your pocket, he turns around = the time is different. You also disable the light switches in the apartment / house. Then you start acting like a dream character, trying to convince him it isn't a dream. You could always include other people to act in this, to make it more interesting.

LOLLLL, it would be funny to watch his reactions, or film them with a hidden camera.

Nonetheless, this shouldn't be attempted if his apartment is 2nd floor and above. He might try to "fly" by jumping out the window.