Still in design phase, but just like it sounds.......some kind of lightweight fan blade extensions, which are easily but firmly secured w/ no tools..........cheap, adjustable, safe.......all that stuff.....
Another idea would be ceiling fan blades that are designed to extend telescopically using the centrifugal force generated when the fan starts running... some kind of very light spring mechanism would retract the blades as the fan comes to a stop... still working on this idea...