The final product is completely made of ABS, except for a single 72-67 step-down ring that provided the filter thread. Unlike the commercial solution, the "base" is not held by screws, but rather by a twist mechanism that locks it into place. It is slightly bulkier than the metal version, but works well. The ABS construction was surprisingly solid, and unlike the metal flip ring (which is heavy) this gadget has slightly positive buoyancy. All by all, after about 12 dives with it I am very happy.
The design can be found here - 67mm frame holder for Nauticam 4 inch wide angle port by nirfriedman - Thingiverse
If there is interest I can also upload it to shapeways and then you could order the printed version directly.