Speakers hung from ceiling on aircraft cable.

David, I did this with a pair of open baffle speakers I made for a friend.
It worked wonderfully however I crossed to a subwoofer at 80 Hz. The
Speakers also weighed 20 lb each. 

The LS 50's are not very big and they do not go very low down. I suspect they will be OK. If you feel them move with bass you can always put a lead sheet on the top of the speaker to weigh it down. I would not use cable. You will have trouble getting the speakers to face in the right direction as the cable is torsionally compliant. Better to use chain it is much less torsionally compliant and will want to stay in one position.

David you are right and you will be absolutely fine. I would do it with just one chain per speaker sized so the speakers hang at ear height.
Even if you did not cross out at 100 Hz you would be fine. The mass of the cone assembly is far less than the rest of the speaker. Imaging will be just as good as if they were on stands and because you are crossing out at 100 Hz distortion levels in the little woofer will drop considerably. It should make a wonderful office system, a lot better than the two Sonos speakers I use.