I found holding the xteink for long periods was just a bit uncomfortable when the light was mounted on the back, so I made a simple case and attached the booklight holder to the back. 

I added a ring mount inside the case, for those who might want to add a ring for magnetic attachment.

The case is just snug enough to hold in the xteink x4 reader while using, but not for permanent usage without the ring attachment.

Also, the booklight clip fits very snuggly into the holder. 

My skills on design are currently limited, so if you can redesign and make it better, go for it.