If you prevent the magnet from actually coming in contact with the strike, the magnet will be more strongly attracted to the cup. I don't think you'll need to glue the magnet in. You could use a steel flathead screw as the strike, make the countersink a little extra deep so you can adjust the depth of the screw. Once you have it set, glue a little piece of thin leather or felt over it. That will hide the screw and add a pad to soften the closing.