how to get texture folder in .mtl


I need the texture folder written in my .mtl file. Right now what i do is: i make all path relative, than unpack all textures in a folder where my .blend file is, than i export the obj. with strip path and copy the folder with the textures in the folder with the .mtl and .obj files. Now i have “map_Kd wood_01.jpg” in the .mtl file. But the client would like to have something like tex/map_Kd Comics_01.jpg to have a better folder structure. How can one do that :)?