Magnetizing a backplate might help a little, but it is made of 4140 or 4150 steel alloy, and won't hold a magnetic charge as well or as long as low carbon steel or iron, and the magnetism could screw up the firing pin's operation.
I've been using R&D cylinders in a half dozen guns for 10 years, and have never found a need for added retention, load 'em, replace the backplate and insert it, everything stays together. When you remove the cylinder to reload it, you want it to come apart easily.