I laser cut/etch a wood veneer to protect the back of the phone. There was just enough space to fit the wood veneer in between the phone and the bumper.
Aluminium bumper (ebay ~$10)
Wood Veneer (1/42 inch thin)
Laser cutter (x acto knife might work too)
40 W Laser cutter setting:
Cut: 90 Speed, 15 power
Engrave: 25 Power,100 Speed
if anyone know where Samsung release dimensional drawings of their phones, do share it. The caliper is used to measure the cutout for the camera, led flash, and speaker.