Began by using a large diameter dowel to roll the upper most (smallest) tabs that form the rudder leading edge.
It's nearly impossible to get any leverage on the end of the dowel closest to the counterweight rib. The large diameter dowel gave things a start, but really didn't do much.
So I went to a smaller diameter dowel to try to get more curl. That worked better, but you have to work the tabs with your hands and not just the dowel, or you will make the roll diameter too small.