Make that s*it holms. You don't need the fancy ribs, just use a flat piece and cut out the holes. If you've got to do the ribs, improvise. All the fun of all that metal work is making things, otherwise it's ripping off someone else's work.
If I were trying to accomplish something different i would do as you suggest and just weld in a flat piece and drill some holes. But i want the ribs and the repair to look factory, so grafting in an original section is my best and most elegant option.
Btw. I don't get the stealing thing....If that were the case what would that make AMD, or anyone who has ever cut in a patch from a donor. :)