GUI.DrawTexture from an atlas with many textures...

Can I define a source rect somehow so I can have all my GUI textures in one atlas and just chop out what I need when I need it? I am thinking this would save on batching?
Is it possible looking at the documentation it has a destination rectangle but no way to define a source inside a texture to use? So I am currently having a different file for all my GUI elements which has got to be eating up call draws I am suspecting...

Wondering if there is a better way?
(yes not on new GUI system still using < 4.6 cause of other reasons)

 

http://docs.unity3d.com/ScriptReference/GUI.DrawTextureWithTexCoords.html

That should be able to cover your needs. Lets you define not only the rect for where to draw the image, but also specify a rect within the texture to use as the source.