I saw this item at walmart yesterday and imediately thought of this how-to. I'm guessing depending on the size/shape/weight of your laptop it might be a perfect match. It'd allow for the swivel, tilt piece too. I saw that the tray part comes off of the arm and uses what looked like about a 1" OD pipe so i'm sure making a tray to suit would be easy.

Auto Swivel Tray Saucer - Home Garden and Pest Control Solutions