An internal combustion engine is like Carol's subjective cold-sensation in her left hand - one way among others to bring about the externally-observable behavior. (By "externally observable" I mean "without looking under the hood".) In Carol's case, that behavior is identifying 20 C water. In the engine's case, it's the acceleration of the car.

The subjective cold-sensation in her left hand should be part of the observable behavior, surely? To mix the analogies, if it were my job to disguise the fuel cell as a combustion engine, I certainly would feel like I had to include this subjective cold-sensation part.

But I'm not familiar enough with the discussions about uploading to know to what extent people intend to make the fuel cell keep the subjectively observable properties of a combustion engine.