I fixed this just now by perching him on top of the external hard drive attached to my Mac. The waste heat from the drive keeps him going, no water required; in consideration of this Stirling achievement, I have dubbed him Tantalus. (I have not yet dared to put a water glass right next to the open drive vents for maximum authenticity.)
With the drive asleep, he "drinks" perhaps every couple of minutes. If I keep it busy, on the other hand, he gets 3-6 (somewhat chaotic) rpm.