Thanks to http://www.thingiverse.com/kittka for the idea of the stir plate!
unfortunately the original design didn't fit my fan's, so I had to edit them.
this stir plate will fit a "DC brushless 12025" computer fan, but you might want to check on the size of the fan hub (mine was 42,5mm diameter).
1x Fan - DC 120x120x25mm
2x Magnets - disk 20x2mm
10x Magnets - square 5x5x1mm
4x Bolts - 30x3mm
1x Fan speed controller
-pause the print of the stir rod, to insert magnets x5 on each side.
-I added some disks on the stir plate corners to prevent wrapping