Summary

This stylish holder will secure your Nexus 5 to handlebars up to 1" dia. See Instructions tab for additional items required to assemble.
It is also available, printed on demand for $38 plus $10 shipping.

Instructions

To assemble it you will also need the following items that can be purchased from the McMasterCarr site. Here are the links:
(1) 18-8 SS Self-Locking Thick Wall Insert .25-20 Int Thrd X .438-14 Ext Thrd X .438Length (2pcs):
http://www.mcmaster.com/#catalog/120/3289/=ri0m0y
(2) Vinyl Buna-N Foam Tape Adhesive-Backed, .188 Thick x.50Width strip:
http://www.mcmaster.com/#catalog/120/3577/=ri0cn6
(3) .25-20 xb.75 long Socket Head Cap Screw with Captive Lock Washer (2pcs):
http://www.mcmaster.com/#catalog/120/3109/=ri0ddn

After printing the top and clamp, thread items (1) into top and secure them with crazy glue.Cut foam tape, item (2), peel adhesive backing and place onto top and clamp components as shown in the exploded view. Secure unit onto handlebars using screws (3).

Nexus 5 Handlebar Mount Holder