Here are some things that occur to me that will help slow the freezing of water, alone each should delay the freeze, using more than one tip should increase it even more. These ideas all assume that you put out fresh water in the morning that is in a container that was kept in the house to warm it prior to being put outside.
MASS
If you put a fresh bowl of water in the run mornings before going to work, a thin stainless dog bowl will freeze faster than say a thick ceramic dog bowl. The increased mass of the ceramic bowl means it will hold more residual heat from inside. The amount of water in the bowl will also add mass, hopefully slowing the freeze. I think the black rubber livestock bowls mentioned above are pretty heavy.
Color
As was mentioned above, the darker the bowl and more sunlight it receives will increase the solar heating slowing the freeze.
Wind
anything you can do to block the wind from the water supply will slow the removal of the residual heat from being indoors. but it will be self defeating if your wind block also blocks the sunlight thereby removing the solar heating advantage.
Insulation
if you have access to some 2" thick rigid foam insulation, you could cut out the foam so the water dish fits down into the foam so only the top the the bowl and water is exposed to the air. You'll have to protect the foam from chicken pecking but the foam should help preserve the indoor warmth for quite awhile.
Shelter
If you can provide some type of clear shelter for the water dish, it will help with wind blocking and solar collecting. I'm picturing something like I see bulk olives being dispensed from in the grocery store. The clear bubble tops with an access hole for the birds to enter.
For a cheap easy to make option, I'd try a the square 5gal jugs that fast food places get their deep fry oil in. They are opaque so would allow some solar heating, they would block the wind and also help hold in the residual indoor heat. You could lay it on it's side and cut an access door in the top of the jug(now on it's side) and place the water dish inside the chamber.
So my thoughts for an ideal would be the oil jug with the foam insulation covered by a thin piece of wood or metal painted black to stop pecking and a heavy thick dark bowl set down into the insulation. Place this watering station in the sunniest spot and give it fresh water in a warm bowl each morning.