Perhaps what we call empathy is merely the other rats acting in their own self interest. I could not enjoy a nice peaceful dinner if some human was caught in some cage writhing in front of me.
But that, surely is because you feel empathy. You wouldn't mind something equally visually distracting, such as an aquarium.
What they should do is perform the experiment where the rats do not have to see the cage mate in the trap, but be aware he is there.
That would reduce the empathy in humans too. If we were as distressed by the abstract knowledge that people whom we can't see are suffering as we are by actually seeing people suffering, the world would be a very different place.