NGUI button: Different sizes for different states?

I have some artwork for NGUI buttons:

Unpressed button:

Pressed button:

I'd like to use them as sprite-swaps for an NGUI button, so I import them into unity and set them up for nine-slices, but as the sprite for the pressed button is shorter than the sprite for the unpressed button, the pressed button is stretched upward to fill the same space as the unpressed button. Is my only solution to just include some whitespace above the button?