Been done already by using a Knog back light, the downside is that it's a bit fiddly, changing battery isn't practical, and water can get in the hole causing likely damaged to the light and possibly the frame itself.
some constructor have seatpost (or seat tube) that are designed to accept certain light, such as the Exposure Flare by making a new body that merged with the seat tube.
Been done already by using a Knog back light, the downside is that it's a bit fiddly, changing battery isn't practical, and water can get in the hole causing likely damaged to the light and possibly the frame itself.
some constructor have seatpost (or seat tube) that are designed to accept certain light, such as the Exposure Flare by making a new body that merged with the seat tube.