How do I pre-wire for in-ceiling speakers and give a clean finished look without installing speakers for several months?
There are low voltage boxes used for stereo equipment that may suit.



These can be covered by blank plates that are then painted to match the ceiling. When you are ready, remove the cover and either attach the device and wire through the box or cut a larger hole for the device.

As an Alternative, you could use a bushing like this, and wedge/glue the wires inside the tube



Then you can fill the center hole with taping compound or spackle. When you are ready, pull the bushing down with the wires attached.