Cropping POT images in Unity Button

Hi,

I am trying to reduce the APK size of my game by changing all images to POT images. Unfortunately some images do not match very good on POT. Hence I have a pretty large transparent space at the sides of these images.

For most UI objects this does not really matter a lot. But I have a problem with Unity UI Buttons as the complete size of the image is take for the button, i.e. a large transparent space that should not be clickable is clickable.

I hope I described the problem clear...

Cropping POT images in Unity Button