We use a 90 watt ceramic 'lizard bulb' over the waterer. It is tied up, and uses a small reflector housing like a miniature of the regular heat lamps. Since it is a solid ceramic fixture, rather than a glass bulb it is less prone to breaking. At 90 watt it doesn't throw a lot of heat, just enough to keep the water from freezing for 8 or so hours. We usually have to swap out for fresh water a couple times a day, but at least it is good for when we are at work and then overnight.
Another thing we did, and it works till temps are below 20*.... we take the heated dog dish and turn it over (ours are plastic), we put sand around between the central bowl and outer edge and just set the plastic waterer on the flat surface created. The heating element of the dog bowl is in it's base, which is now in contact with the bottom of the waterer, The sand we used to fill around the dish helps to weigh it down. The chicks can easily jump the 4 or 5 inches to were the waterer sits and since the waterer is so much smaller in diameter than the dog dish it creates a little standing edge for the chicks.
Brilliant idea!