Solder a female header pin to the neopixels:

• Cut a female header pin to the right number of pins.

• Put solder on the contacts on the neopixel.

• Melt the headers pin to the contacts whil adding solder.

Pull the sleeve over the header pin.

Hot-glue behind the header pin.

Hot-glue in the other end - make sure to have amble room and that the hot-glue touches the pcb.