I found this round Raspberry Pi case at my local Microcenter. I loved the red and see-through case design. I was just going to use an old case fan that I had lying around but after seeing the case I decided that it needed some bling.
I epoxied the washer on the fan and mount the magnets
I got a fan controller mounted both the controller and the fan hooked up an old 12v 2A wall wart I had.
I had to remove the tabs that mount the Raspberry Pi
There was quite a bit of fiddling to get the distance right between the magnets and the stirbar. It seems a little counter intuitive but you cant just mount the fan directly under the case. You need about 3/8-1/2 between the neodymium magnets and the stirbar.
I found that if you are getting a bar that is being thrown, not stirring, or rattling to much try increasing the distance between the fan and bottom of the flask.