Most chrome shops will tell you not to attempt metal work on a bumper because you will simply increase their labor. Your surface has to be perfect before any of the plating starts, or they will be doing multiple layers of copper with polishing in between to fill minor scratches, etc. Any imperfection in the surface will be magnified by the plating process, worse than painting a car black with minimal surface prep - every little flaw shows more than you can imagine. You might visit your chrome shop with your bumper, explain what you want in the end, and see what they say, or take lots of pictures and send them to the shop you're planning to use if it is going to be shipped to and from. I would not do any work without talking to the guy who's going to be doing the plating.