Can you stick a screwdriver though from the hole in the other side and give it a few gentle shocks. there is a lot of friction to overcome on the edges, plus its stuck to the flange it beds up to.
If I were at that point, I would be resorting to sticking the whole thing in the freezer overnight, having 2 people ready so as soon as it comes out hit the outer roller edge with the map torch and the other person tapping the screwdriver with a hammer to try and shock it.