Take the small jump ring you set aside earlier and use it to attach the large jump ring to the top of the pendant.
Take the yard of black ribbon and hold it around your neck to find the right length, allowing ends to tie. Then, cut the appropriate piece and tie the center of it once around the large jump ring.
Use the second piece of ribbon to create two channels for the JST cable and battery. These channels will be stitched on the underside of the ribbon opposite from the JST wires coming from the Trinket. The opening between the two channels will be the place for the connectors to lock. Stitch both channels right next to the edges of the ribbon. Top stitch the other ribbon without channels to match.
Tie the JST cable coming from the Trinket around the large jump ring as strain relief. Then, feed it into the channel in the ribbon. Cut a small piece of extra black ribbon and tie it around the JST cable that peeks through the jump ring, to cover it.