A steel-on-steel hammer blow, with hollow space for the ball head to fall out, might work with some oil. Hammers can produce very strong shock waves in steel - just don't put your finger in the way. This simple method was inspired by the fact that yesterday I had an mechanical pencil's eraser stuck in a pen cap. I tried fumbling with sophisticated ways, e.g., blowing on the end of the cap, but it turned out that a few dozen taps with the index finger is sufficient to nudge it loose.

But if you can't isolate the bolt itself, then it's no use hammering from the side as that will make the problem worse.