Whoops: I thought you were talking about the lower control arm ball joint and spindle...
After you have untightened the nut holding the pinch point together on the spindle, take a flathead screwdriver and hammer it into the pinch point - don't be too aggressive - just enough to loosen the pinch. After it is loose, spray a penetrating agent like PB blaster (whatever you prefer) on the pinch, and you should be able to knock everything loose with one strike from a sledge (or you can place a pry bar between the lower control arm and the spindle and give it a good jolt). I'm no expert...just a suggestion.
Edit: Agreed with dubie2003 - if you are going to wedge the pinch apart with a flathead screwdriver, DO NOT let it strike the ball joint - it will tear the boot...