Texture Splatter Shader

Can anyone give me an idea on how to create an Texture Splatter Shader?

Edit: Basically, a texture splatter is a method to blend textures together on a surface using alphamaps (a grayscale image residing in a single channel of a texture). I need to merge together 2 different textures to create a splattered image of the two that are separate yet blended.

See this shader. For more complex blending using RGBA maps, have a look at the terrain shaders (souce here).