I agree on adding/modifying alternate airports enroute etc. etc., but, that is required by 121.631. I cannot find any such requirement for a T/O Alternate. While it may behoove one to be aware of the nearest airport with appropriate weather to act as a T/O alternate in a given situation, I'm speaking on a strictly legal sense. If the regulation is intended to prevent takeoff from the origin without the T/O alternate it should specify that, instead it specifies the flight may not be dispatched/released.