OK, guess you want more design details.
Easier (?) way: Cast a copy of the cover in clear acrylic -- acrylic casting kits are available online. Depending on the cover's structure, this could be impossible.
Harder (?) way: Start with a thick piece of plexi/polycarb.
Use a circle-cutting jig, flat bit and router to remove concentric rings of plexi from the outer perimeter of the NephRing to form the lip that sticks up through the CP.
Cut the TB hole.
Make 3 supports in the TB case for the NephRing that don't interfere with the rollers, encoder wheels, etc.
Cut the TB lid so the 3 supports are exposed.
Cut the NephRing to match the hole in the TB lid and align with the TB.
Add LEDs.
TB-mounting carriage bolts hold the TB body to the CP, keeping the NephRing in position between the CP and the supports/TB case.
Scott