Ok, so I've studied the rules a bit more, sorry for my confused posts earlier.
But, if I'm reading the control spell rules correctly a successful idea roll will only leave the subject "standing around idly", still an easy target? The dragon would need to achieve a special or critical success on it's easy idea roll to break free from the spell. This would require rolling below 20 on a D100, since the modified idea roll is 100%, correct? A one in five chance of success, while the wizard has a 2/5 chance to roll his POW vs. POW. Maybe I'm still confused, but that's how I interpret the spell.
If that's the case I would houserule out the need for a special or critical success and just let the subject make another POW vs. POW to break free or something I think.