Sorry if I'm missing something here, but after you have found the joists, how are you going to get a cable through them if the punter doesn't want you to lift the laminate, and doesn't want the ceiling peppered with holes? Are you planning to put all the downlighters within the same joist and point them in random directions, or is the ceiling suspended with some space above the joists to run cables?
My tip for looking in tight spaces is a bit of broken mirror tile and a head torch. If you shine the torch on the mirror and angle just right you can see what you need to. Not sure the "Elf N Safety" nazi's would necessarily approve of carrying broken mirrors in the toolbox though. I like the thermal imaging camera and endoscope ideas though
