I think JRRDW had the best idea; launch the spool without anything added to it. At launch you need to get the spool spinning so that the wire is deployed of it's own accord and not by pulling on anything. You might take a look at devices for throwing things with a spin like CD and Frisbee throwers.
One advantage is that the only thing coming back down is the spool which shouldn't be all that much a safety hazard.
