A basis guide to how I done it would be
* Get four 3mmx1.5mm neodymium magnets, some super glue suitable for metal, a pair of needle nose pliers and a screwdriver with a rubber handle
* Remove the back plate and place face up on a piece of card.
* Squeeze a small amount of glue into the screw hole recessions and put the the magnets in, apply pressure for 20+ seconds to ensure it is in there firm.
* Clean the excess glue with a solvent
* Screw in the screws about half way into the threads on the mod and use a pliers to gently wiggled the thread bases out (they will come out eventually)
* Get a thin file and gentle file the top portion of the holes until they are the size of the magnet (must be a snug fit).
* Fill the holes with super glue and gently push the magnets in by pushing then tapping with something like the bottom end of a rubber handle screwdriver
* Clean excess glue with a solvent if you made a mess