Suppose you keep your camera at, say, 20 degrees C at a relative humidity of 60%. This means that the air inside the camera will have the same humidity at the same temperature, the relative humidity will increase if the camera cools down. Then you go outside for several hours where it is -20 C, put your camera on a tripod. After some time the camera will cool down and you will get condensation inside the camera.
The only thing I can think of is to go outside with the camera a day or so earlier, remove the lens and let it sit there for a while, making sure no dirt or snow enters the camera. Then you put the lens back on and put the camera in an airtight bag filled with the outside air. You only get the camera out of the bag the next day when taking pictures outside. However, removing the lens while outside seems to me like a dangerous thing to do, you are bound to get dust inside the camera...