sorry, I was just talking about the basic premise for the setup. There probably is a way, but after thinking it over, I don't really know what it is. but this metod works.
right click on your object (or for just the two faces), and 'material'>'new material'>'layered shader'. Then, using the hypershader, create two random materials (whatever it was before that you were using, as in phong or blinn, or whatever). With the hypershader still opened, navigate in the attribute editor until you get the layered shader again. it looks a little bit different than the interfaces for the other textures. Now, middle-mouse drag the other two textures you created into the part of the layered shader window that says 'layered shader attributes' - there should be one block already in that portion (in mine its green). When you drag the other two textures in, they'll create two more blocks, just they should be blue, with a dot in the middle. Hit the x below the first box to get rid of it. Then, to animate the change, simply change the alpha setting on the upper texture (as you would key just about anything). I don't know if it'll make an exact transistion like a ramp between to colors would, but it'll work.
Note here - the nice thing about using two different textures like this, is you can do things like make one layer shiny, and the other not shiny.
If you have any other problems, I know maya has a little tutorial on layered shaders imbedded in the help files. A quick look through there will find it.