It's funny you should ask that, i've actually been wanting to do that for a while now since its pretty easy to do.
The only issue im having is getting the 3rd brake light out from the backseat area.I managed to loosen it but not take it out and i am certain if i try harder something will break.
OMG after reading the instructions and spending about a min to take it out i feel like such an idiot (I read your post here at my work, went to my car right away and gave it a try). It's very easy to take out and i think it will also be a very easy LED retro.
When i get the time to do a quick prototype i will let you all know.