there are many ways to finish off a corkscrew. if you are quick you can bind the tip at the end with the running end of the string in your non-throw hand and do a gyro flop. if you are just trying to get the top to tilt at the end (in other words, go from a vertical top for the corkscrews to a horizontal top) it should do it almost automatically. i mean, i've never really noticed how it happens, but the top always tilts at the end for me. (you can even see in ta0's trick video that it naturally tilts throughout the trick). i think it may be because at the end my arm naturally stops revolving around the top and by making a slow wide arc at the end it causes the tilt. usually i try to avoid this and just pop the top back to my hand, so i try to correct any tilt at the end for a good catch.
i know this isn't much help, but i never had the problem you are describing.