Deployed my trick for running cables down stud walls quite successfully again.
Find the horizontal noggin, inwards-angle-cut a small rectangle of plasterboard out about 5cm above it (such that it forms a “plug” that can be re-inserted afterwards).
Use a small (16mm-ish), long spade bit to drill a hole downwards through the noggin for your cables.
Use rods and rope to get down from the loft above to the noggin, and then down to the faceplate.
Replace the plug and plaster over like nothing happened. Easy.