The rare earth magnets that I got at radio shack were a little small, but that is all they had. I'm not quite sure if they are big enough to spin the bar though.
Here is the potentiometer. It is a 5k ohm and it has the same 90% offf 10% sensitive problem, but it works for me.
And here is the stir plate in it's nice little package. I just need to drill a hole in the front to put in the potentiometer.
It's not perfect, but it spins!





