If you were to do this you would have 23 and 3/4 inches with no taper and the last 3/4 inch of thread would have 3/4 inch per foot taper.It would be very weak and easy to break and if used a violation of 344.42(b).
Thanks Bob,I agree that you could make an all thread but I do not believe that the all thread would meet the requirements of 344.28.In other words it would not have the required taper,I have seen it done before though so you have a very good point.