This is easier in 2D Toolkit 2.0, as the animator there is separate from the sprite class, i.e. you can create your own sprite class and animate it independently. You can import the sprite animator alone from tk2d 2.0 beta and use that, if you want to.
Once you've duplicated the tk2dSprite class - you want to calculate and set mesh.uv2 wherever mesh.uv is set.
uv2 should contain the uniform UVs relative to the base class which you're going to use to position the detail texture. I suggest starting with just a planar mapping, and then working from there.