An idea I had from back when I was in the HVAC trade, use a 3/4" fitting brush, the kind to clean the inside of copper pipe fittings, and attach it to a cable or something fairly flexible, and chuck the other end in a cordless drill, the wire bristles should grab onto the hair of whatever kind of critter is in the duct, then you either pull out the critter, or a ball of hair.
I like the direction you are going but maybe we gould go a wee bit further.
Take the tube off your gas powered weed-wacker. Most of them are cable driven from the engine to the attachment. Now make whatever sort of midevil torture device you can think of, attach it to the end of the cable & crank that bugger up. Arrow broadheads? Pack of blackcats? Endless possibilities.
