Grab a strip of fabric at least as long as your NeoPixel strip, and a little longer is fine!
Sew or fold it into a tube that's just a bit wider than your NeoPixel strip.
Use a needle and thread to sew the 3D printed parts to the fabric, sandwiching the NeoPixel strip.
Sure, you could glue the NinjaFlex on with Permatex 66B silicone adhesive, but sewing gives a delicate finish and makes your NeoPixel strip reusable in the end!
Continue down the length of the NeoPixel strip, tiling on more 3D flexible pieces as you go. You should stitch while the strip is off in case you accidentally pierce it with the needle-- strip is illuminated in photos to demonstrate the diffusion.
You may find it easier to use two needles as you sew along the length of the bandolier or belt. Join the ends of your sash, then knot and cut your thread.