The only way I know of...and VERY carfefully at that, is to get ball bearings with graphite and push through the shaft after heating and straightening by hand as much as possible.
And the main caveat to that is to be able to seperate the shaft from the base point which attaches to the radio. Regardless,it's very difficult and the only time I've done it was on and old radio that had a hidden antenna. My dad did it several times and I can tell you the language used during the process was unsavory at best.
There still will be kinks however, those will not come out.