If you don't have an impact gun, check with your local auto parts store. Usually they have an electric impact wrench for pulley changes and it would only take them ten seconds to pull it for you.
I was able to use a medium small sized flat blade screwdriver and slid it into the fan and locked it against the housing.
Wasn't pretty, and it bent the screwdriver but it worked.
It was a good Klein screwdriver too.
Other than that you need to lock it somehow and use a lot of torque on it after penetrating oil is used sparingly, you don't want that stuff anywhere near the inside of the alternator.
If you don't have an impact gun, there is an hex hole in the end of the shaft in which you put an allen key to keep the shaft from turning while you use a closed offset wrench to loosen the nut...At least that's what I did with mine to take it apart to send it to be chromed...
'bye! Claude