In Fireballs we use something magnetic instead of a fishing lead. Once the magnetic weight (bolt, screw, etc. ) is passed through the sheeve you can slowly drag it down the mast using a magnet on the outside. It is tricky but it does work and will ensure that the halyard is not wrapped around other lines. It also works when the mast is horizontal. I heard that they used a mouse in olden days with a line tied to its tail...