The solid metal grille makes it a challenge. Do you have tools to drill/grind such small parts? I see Aoshima made a 1:43 diecast Knight Rider that comes with an LED scanner. Over $100 so kind of pricey but perhaps you can make inquiries and someone has posted interior photos of how they did it - might give you some ideas. A simple web search amazed me on level of interest in these models including the LED scanner; in other words I'd think there are others out there who tackled the exact problem you're facing perhaps on a car-modeling forum? Here's a youtube I found showing the Aoshima LED scanner in action: