The Microswitch Removal Method
This is definitely the most drastic work-around. It involves opening your camera and removing or disconnecting the small switch that is pressed by the NightShot mechanism. This effectively allows you enter NightShot mode without the camera knowing about it.
Although very effective, this method renders all other NightShot functions inoperative - such as the NightShot LEDs on the front and the HotShoe functionality.
If you are brave enough to open your camera and don't care about other NightShot functions then you may consider this. I cannot at present provide detailed instructions for doing this and actually I don't recommend it because of the risk of damage to your camera.
Be warned that this method may invalidate your warranty - do this at your own risk.