I'm looking to do the same. To take it a step further I'd like to be able to cycle alpha maps at runtime. Is there a way to point to a variable in a .wdl from the .fx file so I can assign the alpha cycle to a button? So all in all there would be 3 images; material, alpha map and the cubic environment map.

To expand it even further, could you have an environment map and texture map for each alpha seperation? So the layout would be

alpha ---> texture 1 <split> texture 2
|
---------> environment map1 <split> environment map2

Basically, I want to be able to take a model and apply a basic texture to it. Then the player can cycle through different patterns or logos and apply them to the model via the alpha maps. Also, the player would be able to change the RGB values for only one of the alpha splits. Thinking in black and white, the white part of the mask can change the materials color.

I'm not looking for a full written shader. If someone could just point me in the right direction or give me something to work off of that would be fantastic. I hope I made everything as clear as possible. Any help would be greatly appreciated, thanks!