But you just don't listen, you encourage. In my opinion its quite like the situation I described.
Not really encouraging to hear him out, you've got a very low bar. In case you haven't noticed, the opposite approach hasn't exactly discouraged. If anything, the opposite: the adversarial approach makes people instinctively react defensively, and cling tighter to the idea. What do you expect? If you're mocked, your reaction isn't going to be "Ah, yes, you're right, I
am deluded/narcissistic/mentally ill/should die," it's going to be "Screw you."
Simply listening to the idea isn't going to make him believe what he says more than any other behaviour. What it does do, is allow for actual back-and-forth, rather than insults responded to with understandable defensiveness. I get to understand what it is he's proposing, and hopefully he gets to derive a little enjoyment, as well as being able to dedicate more time to the less cliche discussions and topics.
I would be very interested to hear what benefit you imagine ridicule has. If we accept your analogy, is going up to someone with paranoia and saying "You're an idiot, there's no one following you, you're incapable of any rational thought, and you should lock yourself in a vacuum chamber and suffocate to death," any better?
At least it predicts there will be eclipses. In scepti's speculations (please stop calling it a model) the sun we see is a reflection off the ice dome and the moon is a reflection of that reflection.
Good luck working out how you get an eclipse out of that hot mess 
No offence, but I'm going to listen to Scepti's phrasing of it. Maybe you're oversimplifying, maybe there's an element omitted... To begin with, there'd be the set-up and properties of what it is that's being reflected.