This may sound a bit out there but I believe it may be possible that a retractable sunroof could be hidden in the design of the windshield! There aren't many pics of the windshield-roof transition but from what i've seen, it looks seamless - like the windshield flows as a single piece of curved glass right up to the rear falcon door lines. There is a panel (moon-roof) above the driver/front-passenger area. Since there is no firewall between the fronk and cabin, it would be theoretically possible to slide the entire windscreen down into that cavity so that the moon-roof panel is open, no? The geometry of the windshield - smooth continues curve - may make that possible, but hard no determine if it tappers at the top or is parallel top to bottom from available pics.
Just a thought ..or more like wishful thinking