I just pulled it out completely and examined it. It is bonded around the entire perimeter either with a friction plastic weld or using a plastic adhesive. You'll have to separate the front from the back just to access the place you need to put the light(s).
The LED solution will need someone to fabricate two circuit boards and those circuit boards will need to be electrically connected to the one board already inside the assembly. Toyco was not nice enough to give us an unpopulated board, there are LEDs where the board is, and there are none where it isn't.
I'd want to buy another one to split open and do the development work so I would not be driving around with a hole where my CHMSL is supposed to be. I bet the light assembly is in the $150 - $200 range, so it looks like modding this piece is both not simple and not exactly cheap. I'm thinking another $150 - $200 on top of the cost of the light to make the rest of the thing light up, unless someone can get the component pieces from Japan, build the extra parts and do final assembly here. Even then, it will be a significant investment. I'll have to think hard about this one...