I made it sole and just used the original grill as a template and cut the S4 one with a Dremel type tool. The bottom was secured by the original clips and the top with two very small cable ties, that secures the grill to the surround, from memory it then clips into the bumper as normal and used two tiny self rappers to secure the top of the grill to the bumper.
Mine doesn't move about and you don't see any of the screws/ ties atall.
I know some have mounted the grill to the surround with hot glue but I used the above method as I remove mine periodically to repaint the surround. Hope this helps.