Hypothetical Question!

In the absence of using a high quality switching box to test cables I believe that your method will work given that sonic differences will be heard if there are various things that remain the same. Ex. - say if your room is square and your speakers are identically positioned from your listening post. I do not forsee any potential damage as a result of this method. I try and do it this way as my sonic memory is probably not as fine tuned as others'. I am more apt to hear differences switching from left to right then trying to remember what something sounds like after I have spent 5 minutes or more changing cables andf replaying a specific song. I am sure that other posters will expand on my position but I think you are on the right track...

Your experiment won't damage your equipment, however, I doubt it will reveal much about the cables. First, your listening room would have to be absolutely acoustically symetric. Second, you need to listen in mono. If you use a stereo source the speakers will not have the same input signal. Third, since you are only listening to mono, the cables stereo performance will not be revealed.