Hi! You want two options:
(1) On the Scales tab, choose Manual.
(2) On the Options tab, check "track for each scale (advanced)".
Just to warn you, though, a druid with all four specs will see a lot of green arrows with those options set. If it becomes too much work, consider unchecking the two specs you're less interested in (by shift-clicking), assuming one's feral/guardian and one's balance/resto. You won't get the ideal, perfect item at each time, but that's not too important when leveling. I hope that helps!