Unless I missed something, more insulation and ventilation is going to promote uplift, not lessen the effect. It is the difference in the temperature and humidity between the top and bottom chord that creates the phenomenon. If you want to stop the movement, take out the insulation and allow the top and bottom chord to be the same temperature and humidity level.
Bill, removing the insulation would reduce the difference in temperature and humidity, but you can't do that and still comply with the building codes (or common sense).
I would think that moving the insulation from the attic floor to the bottom of the roof to create a conditioned attic space would have the same effect... but that would take some work on a completed structure.
Providing a slip joint as Jerry and others have mentioned is going to be the easiest long term fix.