How to do it with texture_shader & register_combiners

I want to use depth sprites with four (or at least three) textures combined in it. It is for GF4, so i must use dot_product_depth_replace which takes 3 stages in TS. tex0 hold the depth information. What if i bind textures to tex1, tex2 and tex3? Can i use texture coordinate for color lookup in tex1 from tex0? If so how it will be writed in vnparse code? I mean something like this:
TEX R3, fragment.texcoord[0], texture[3], 2D;

And just another question. If I want to combine the same texture twice just applying different texture coordinates, is this possible with register combiners from one texture unit? Of course this is possible and (probably) easily may be implemented when use two texture units with binding the same texture for both… but what about using one texture unit?