Nintendo confirmed the existence of the controller to Eurogamer, declining to offer any more details. No GameStop listing was found for just the controller, leading us to suspect that FlingSmash was always intended as a pack-in with the Wii Remote Plus (its Wii Play, so to speak) -- which neatly answers the question of why Nintendo would make FlingSmash a full-priced retail game. We're contacting Nintendo for more details, since it probably knows a bit more about its own release plans than GameStop.
Update: Nintendo has "nothing to announce at this time," a representative told Joystiq.