Mask or progressive showing of GUITexture

I'm using a GUITexture to show stat bars (such as HP). I've seen good explanations how to use materials to progressively show GUI elements:

http://answers.unity3d.com/questions/14770/creating-a-circular-progressbar-timer.html

http://answers.unity3d.com/questions/173375/progress-bar.html

however, I'm not having much luck with applying that since GUITexture doesn't have a material, but only a texture.

So far, I'm most probably going to use atlas of 10 textures with different percentage values (0%, 10%, 20%, etc), and I'm just checking is there a way to apply a mask to GUITexture that I'm not aware of.