The shell will be fine. My guineas hatch and they have incredibly tough shells. I dropped a guinea egg on the ground once, and it didn't even crack or dent it. To make it more humid, you can get a washcloth wet with boiling hot water, put the cloth in a dish, and put it under the pad. Mist the eggs very often with warm water too. Thats really all you can do under your circumstances. An incubator or broody hen would be best, but if none are available you'll just have to make do. Keep me posted. I hope he hatches! Playing duckling peeping sounds is really good. Tapping on the air cell mimics the hen, and encourages the duckling to pip. Are any of the other eggs alive?