It is hard to believe that Porsche just relies on friction to hold the shifter knob in place. It is counter-intuitive to think that you have to twist and pull so hard on the shift knob to remove it. I was sure there was something I was missing, as I'm used to removing set screws or clips to remove accessories. After reading articles assuring me that I just had to twist and pull hard, I found that the shifter knob was extremely tight and I was afraid I was going to damage my shifter assembly.
Kudos to Gcalex for coming up with the vice-grip plier suggestion. I used your suggestion o