In the very first post in this thread is a video of the T3, and at about 5:55 it shows how the cover is removed and what is then left. I think your only choices are to keep the original cover that you purchase with it, or buy the additional cover with the light and swap it out as the video shows.
https://www.mobileread.com/forums/sho...d.php?t=221532
I still think they should have sold the reader 2 ways, 1 with the basic cover without a light, and 1 with the lighted cover only. For those who will want the light, they've paid a higher price for a cover they can't use for really no reason.
Edit: Another good video here, although the review is in German. But you can easily see how the cover detaches and how it looks.
https://www.mobileread.com/forums/sho...d.php?t=221966