A heat lamp would be great, but be careful about how close it is to those shavings, don't want to start a fire of course. Do you have a thermometer you can put down next to the eggs to monitor the temperature? They should be kept right around 100 F if at all possible. You don't want them to get too hot, that is more dangerous than too cold. And this is just until you can fashion some kind of incubator that can also have some humidity as well. Humidity is very important for duck eggs! ;)
I'm really not experienced incubating eggs without a real incubator or a hen, so I don't have much more advice on how to build an incubator yourself. I know there are threads around this board on it, though. I've heard of people using coolers and adding bowls of water for humidity.