Until recently.... I managed to covertly get this thing into the car, along with both boys, drive to a gas station and inflate it without Evan noticing.
When introduced to the ball already fully inflated and looking rather stable (his biggest fear is that it will spring a leak and fly around the room) he acted indifferent about it, but at least not scared. After a week or so and after a few friends came over and thought it was fun, he has come around.