I agree that using the knobs/sliders is the only current solution as well as a good way to force you to mix with your ears rather than eyes. That has actually happened naturally for me, and I almost never use the graphical display anymore when setting the eq, in part due to having an external controller with an eq-section.
But, I do still think that a fine tune mouse mode for the graphical section would be a good feature, since the modifier keys are already in use one solution would be to use the right mouse button for it.
/A