Oh, right, people seemed to complain about this a lot. I have no clue why, but perhaps they don't know much enough of the Freeze Enemies event mechanics. The way to do this is holding both shoot and jump button (and right arrow key) all the time and it works. However, it's possible that it somehow depends a bit on the frame rate (didn't test it much, but I recall that passing this varied slightly on my old PC running JJ2 on 30 fps). Basically I think that the more fps the later you get free. Nothing sure though.