The C5 should be very nicely "stealth profiled," as long as you don't have your iceburg headlights up.
You really shouldn't need a bra.
Certainly, a front plate would cause a tremendous PT concern, but I don't imagine that you have one?
If you are really concerned about things, go a step farther, and VEIL the exposed front-end lighting elements.
With the Blinder heads, 3M Automotive Trim/Molding tape will effectively hold them "permanently" (while still allowing for fully residue-free release, at a later date, if-desired, with no damage to the vehicle finish, provided that the vehicle finish in the mounted area and immediate surroundings were not damaged at or before the time of application, to begin with). Pay good attention to initial prep (cleaning the area, as well as with proper consideration for surface temperatures), and you'll be fine.
Shimming the heads can be achieved with any number of different methods, and is limited only by your imagination.
Remember to get the heads as level and square as you possibly can - obsession here really counts.