Unity 4.6 new UI. Resizing image in Scroll Rect

Hi everyone,

I have been fighting with this problem for some days, and I would really appreciate some help.

I want to create a scroll rect using the new UI system, that fits the upper part of the screen (so I anchor the Rect transform tu the upper part, etc...) and independently of the screen size, to have a certain amount of buttons inside the scroll rect.

I have no problem at all, except for the size of the buttons. I want them to stretch vertically but maintaining their aspect ratio. If I set this option to true, then they don't stretch.

You can test this in the "Scroll View" scene in the example project of the new UI. How could you impose that the buttons resize vertically, maintaining their aspect ratio?