Temporary pinning of sensors to ceiling
Double-sided carpet tape, or blue tape protecting both surfaces with superglue between. (If the ceiling is popcorn, neither of these will work.)

If you have a popcorn ceiling, I'd experiment with thumbtacks superglued to tape on the sensor. My suspicion is that 3 tacks would hold and not make too much of a mess of the ceiling, but you'll have to do a bit of trial/error.