Cut a potato and.......oh that's for a broken light bulb.
Seriously, the first thing I'd try, is go and shoot a 100 rounds and get it good and hot. While its still cook'n try to loosen it. If that does not work, get some PB Blaster penetrating oil and soak it down real good. Let that soak overnight and try it again the next day. For better leverage, put the choke tube wrench in a vise and turn the gun. Seriously, it works.