I went looking for a pic and didn't find it. IIRC, he would hang the frame on a stick through the bb shell. You can bend a bb shell, but if the stick is about the same size as the shell then it will not bend enough to notice.

Someone said one of the pneumatic chisel/hammers would work. I bought one from Harbor Freight, and it did nothing. I feel like you could set up a slide hammer to pull. A stick through the bb would be a good idea. At this point I think you need impact or brute force. But it might not be a lot of force.