Since you gotta be working up high for a while yet, don't forget those aluminum ladders get pretty slippery with any ice or snow....
Maybe you could rig some sort of pully system or anchor off of the gable end that you could tie the safety line to before you get the siding on the outside of the house? Then take it down when you put up the last piece of siding.
Regarding safety lines, take a look at some of the safety harnesses or vests that they have for deer hunters that hunt out of a treestand. There have been injuries caused by falling with just a safety belt.