The black RTV silicone has many many uses. Aside from it's usual gasket-sealing job, it makes a perfect alternative mounting option.
Simply apply to the rear of any grille or hideaway lighthead and allow it to set in place. Once dried it forms a tough yet flexible adhesion with no adverse effects to the body work. Once it's time to remove the lighthead, simply glide between the LED and the surface with a sharp blade to remove. Any excess silicone on the mounting surface can be removed with a fair rub.