i would glue the plate about 6 inches up and maybe another plate 12 inches up
Got it. I think this could partially work, but not perfectly. It will depend on how high the magnets are (12 inches up will work a lot better than 6) as well as on the force of airflow.
A strong magnet (no idea how to measure magnet strength) would probably hold the shade relatively still for most normal breezes, perhaps flopping gently in and out between the magnet point and the top. A strong breeze might pull it off the magnet, but if that's not too often you might be happy enough. In addition to a natural strong breeze, negative pressure in your house could also pull the air in with more force, e.g. cross-breeze if another window is open across and/or you have an exhaust fan.
Are your roller shades cheap or expensive? The cheap ones will definitely start to crack and tear after a while from this. Maybe a second magnet at the center point could give more support