Solder a JST battery connector to the pads on the back of your Pro Trinket.
Hook it All Up
Decide where on your boots the Pro Trinket will live. You may want yours on the inside (for slickness) or the outside (for rocking your cyber style). Be sure the battery port and USB port are accessible, and be sure the reset button is safe from accidental squeezing when your boots are on.
Poke the wires from the NeoPixels and the sensor through the boots so they all happily meet at the Pro Trinket. Flex the boot a bit and make sure you have enough slack in the wires that they won't break if you dance too hard.
Solder the wires on according to the wiring diagram. Take your needle and thread and stitch the Pro Trinket to the boot so it stays securely in place.