You can borrow a tool like this from Autozone or Kragen etc.

http://tinyurl.com/yd87pfn

A little more elegant than wacking with a pickle fork....just tighten the bolt with a breaker bar until you hear a big snap...don't worry, nothing broke, the tapered part of the ball joint just popped out.

Should work with knuckle still on the van (in this photo I had also removed the lower ball joint)