My Aviators never quite fit properly behind my ears, so this is my solution for a more comfortable fit. You can easily make your own for any type of wireframe glasses or sunnies (best for wire arms with a diameter of 1.5mm, although you could scale the print or simply drill the holes out to fit your frames).
Simply cut the arms off, leaving 15mm of length to slot into the holes of the new 3D printed arms. I used Araldite to glue them into place. Make sure you try them on before gluing, you want to get a good angle on the arms so that they wrap around your head behind your ear.
For full details and images of how I made this item just visit my blog https://edditiveblog.wordpress.com/2015/01/05/3d-printed-arms-for-sunglasses/