I've not tried any additional dampening on the D7100's cups, but I've taken a look inside when I had them. There's precious little room in which dampening material could be inserted - the driver almost touches the raised center of the earcups - and in the lower portion of the cup there's already some dampening material. I suppose whoever decided to put it there didn't just leave out the upper portion for no reason. But perhaps it would be worth trying. Here are some pictures of the earcups:
On a side note, I miss the comfy earpads of the D7100.