I installed a series of four of these (http://www.ikea.com/us/en/catalog/categories/departments/lighting/18750/) in a plaster ceiling (old house) off an existing hot-switch outlet light switch. Fortunately the wall/ceiling joint above the switch was below an upstairs wall. I removed the baseboard upstairs, opened the wall such that the baseboard covered the hole and fished the line through that 90deg bend and out into the center of the room along the ceiling/floor joist gap. The joists ran the width of the room so wiring went to the middle of the room to one of my fixture holes with no obstructions. I marked the joist locations and helped my customer select the best locations for the lights. Two of them ended up being next to joists and were easy to secure. The other two required spanning hardware, which is relatively easy to mount through a light-box sized hole. I traced the hole locations using the actual light boxes, perforated the traced circles with a small masonry bit on a hammer drill, and gently knocked the plaster circles out with a hammer and chisel. Fortunately I was able to avoid plaster cracking, which I told the customer would be a risk. Through these holes I was able to drill wire holes in the joists using my cordless, 1/2" wood bit, and bit extenders. This can be tricky but not impossible. The rest of the job was fairly standard.

I charged $300 for this. Probably should have charge more but it was for a close friend.

As for the hot switch plug, I replaced that with a new intact plug and put wire nuts on the remaining wire at the plug and at the switch. Not much more you can do without tearing walls apart.