The 2020 mount piece can be secured to a 2020 extrusion (as seen in the pictures on my Folger Tech 2020 Prusa i3) using a t-nut and M3 bolt. The camera holder will fit snug over the ball joint, allowing one to adjust the camera's position easily. The camera holder can be printed without supports if your printer can bridge well, if you have the front side (where the camera lens pokes through) flat on the build plate.
Technical
(1) 3D printed camera holder piece
(1) 3D printed camera 2020 mount piece
(1) M3x10mm bolt
(1) M3 T-Nut for 2020 Extrusion
Nice case! Making a case for a RPi camera is fun, I have made a few. I really like your use of the ball joint, this will provide great range of motion. I also like you implementation to utilize the track structure of the 2020 extrusions, plus the camera can pop in and pop out easily if needed. A lot of great ideas here all in one! EPIC!