Reddit reviews Niner Bikes YAWYD headset top cap, 1-1/8" threadless

• Put the stem as high as you think you'd ever want it (as shown in your photo), then using a sharp implement, score the steerer all the way around using the stem as a guide. Remove fork from bike.
  
• Cut the steerer so that it will be 3mm shorter than the top of the stem (depends how close your mark was to the stem here). This will give the space needed to pre-load the bearings. (You can also cut it flush and use a 5mm spacer on top of the stem).
  
• De-bur and install star nut.
  
  
• Ride bike, adjust stem position, ride, repeat, etc. Find where you want that stem positioned.
  
  
• Cut again. Make sure to tap the star nut down a bit and/or measure so you don't cut into it.
  
  
• Install YAWYD top-cap with bottle cap of choice.

If he also likes beer: https://www.amazon.com/Niner-Bikes-YAWYD-headset-threadless/dp/B00BGDNT5S/ref=sr_1_1?ie=UTF8&qid=1466011107&sr=8-1&keywords=niner+beer+top+cap