I cut the PVC tube to match the width of my keyboard (256mm), then drilled the following holes:

• 3mm hole in the center of the middle of what will be the top of the tube, for the two prongs on the bottom of the LED.
• Two 1.5mm holes 105mm from the right hand end of what will be the top of the tube, for the two prongs on the momentory button (I cut off the other two prongs).
• 2mm holes, 15mm in from each end and close to the bottom edge of what will be the front face (side facing keyboard), for the piezo sensor wires.
• 2mm hole in the rear side (away from the keyboard), for the PCB screw. Mark the correct position using a spare PCB.

I sprayed the tube with matt black enamel paint to match my keyboard. Some pictures: