When it's really cold, there isn't much you can do. Afterall, when water freezes, it freezes.
On those borderline days when ice is in fact forming but you can still fight back a little, try a roof shingle. Note that the sun has to be out of this to work.
Slit it from the edge inward, and run your line through the center. It will draw in enough heat to keep the temp that critcial few degrees higher, keeping your hole/line trouble-free longer.
Block slush from blowing in and gathering on the line and in the hole by setting a wind-break on the windward side of. It doesn't have to be more than 10-12" high, as all the snow is close to the surface of the ice. A piece of rectangular wood paneling works fine. Heaped snow works also.
Keep using the Wind-Las: they're super-deadly. Best of Luck.