This just doesn't seem feasible to me. The fishing line idea might be do-able, but would probably not look that great. There's also the issue of the speaker "swaying" in the breeze. Does anyone know if the expulsion of air due to the vibration of the cones would make the speaker sway? Physics tells me it would, but I guess it would depend on the mass of the speaker relative to the force generated by the wave coming out of the speaker cone.
If you are willing to engage in pre-listening "set up" - (i.e., engaging the surrounds by "unretracting" them) - then why not simply run some bare wire to the speaker, set it up on a stand, then store it close to a wall. Move it out into the middle of the room only when in use.
I guess I'm not very creative, but your solution sounds like a very complex (and expensive) custom job.
