Is this possible, I assumed it would just be an option.
Try searching for “Unlit Transparent Shader” on the list. Here are a couple of hit that had shaders that were in the right direction:
http://answers.unity3d.com/questions/18173/unlit-transparent-shader.html
http://answers.unity3d.com/questions/189695/add-color-property-to-unlit-alpha.html
I use the one that came with EZGUI, so unfortunately I cannot post it to the list.