Setting locked track constaint to be linked to active camera


I’m using the locked track constaint to make an object(a 2d texturized plane) look at the camera. My question is if I can make the constaint linked with the active camera not a especific object? So when the camera changes in the animation, the locked track constaint will change according to the active camera.
I’m using the Camera changer script to change the active camera and simulate a batch render with yafaray.

Or maybe if I could make an object copy the location of the active cam would help too.
So I can link the constaint to this object.