The way I rigged my my magnets was to glue a large steel washer to the face of the fan. Then I just stuck two of the little round neomidium magnets to that washer. I can send you a series of pictures off line if you'd like. I'm new to the forum and am not real sure how to post a pic into my...
Also what volts are you putting into the rheostat? I had a 12V power supply going into mine the first time around and it got super hot. It also spun the fan too fast which made the stir piece keep flying off to the side. I changed my power supply to a 5V old phone charger and that slowed...