I couldn't find a spring with the right tension to make EvilSpyBoy's spring loaded sharpie holder work, so took his design and modified it to use some 12mm rare earth magnets I had.  Works nice and smooth now!

The top sleeve is design to thread a 1/4 -20 screw into it.  Just toss a magnet in there and it will stick to a screw.  Put another magnet in the pocket of the sharpie holder sleeve, making sure the polarity is reversed from your other magnet.  You should be good to go!