I've had excellent results bending Pachmayr Old English pads to fit a curved butt. I just heat them up using very hot water to soften them up and bend them by hand to match the curve. If you go at this slow the base will bend and not crack. It may take a few heatings to get the result you need. I would also suggest sanding the back of the pad to give a good,flat surface to start with.

Doug Mann