Sam is referring to the long rectangular Pininfarina empblems on the rear flanks of the series 4 cars. As to your original question, Sam, you can access these by loosening the carpet on the sides of the convertible top well directly behind the seats. Remove a couple of the black finishing screw/washer combos. There is a vinyl flap that is glued in place at the top of the well to conceal the cavity itself. Pull that flap loose (you can re-glue it with 3M spray upholstery adhesive), and you can reach down into the cavity to the back of the studs. You can use small "speed nuts" or the round push-on retainers ("push nuts") commonly sold in hardware stores.
The body shop quality double sided emblem tape is indeed very good at this kind of thing, also.