The stickiness/softness/runniness of nougat is directly controlled by the temperature you heat the water/sugar mixture to. The higher the temperature, the less runny the results will be. Once you've mixed in the egg whites, though, you've made your choice, and can't later decide to make it thicker.

It sounds like you want two different materials: a hard nougat for the outside, and a soft nougat for the inside. Perhaps you could make two batches, and diP blocks of the softer (heated to a lower temperature) into a still-melted bowl of the latter? It might be tough to get it all to work, though...

The stickiness/softness/runniness of nougat is directly controlled by the temperature you heat the water/sugar mixture to. The boiling temperature of a water/sugar mixture depends on how concentrated the mixture is; the more sugar per amount of water, the higher the boiling temperature. As you evaporate the water the mixture will get more concentrated and the boiling temperature will rise. So, the higher the temperature, the less runny the results will be. 

Once you've mixed in the egg whites, though, you've made your choice, and can't later decide to make it thicker.

It sounds like you want two different materials: a hard nougat for the outside, and a soft nougat for the inside. Perhaps you could make two batches, and dip blocks of the latter (heated to a lower temperature) into a still-melted bowl of the former (heated to a higher temperature)? It might be tough to get it all to work, though...