If there is not a huge amount of ice on the lock,just cup your hands over it as much as possible and breathe on the lock for a couple of minutes.It's slow but it works if the lock just has a little ice inside and not a huge covering of ice over it. Did you ever try putting a sandwich bag over the lock and using an elastic to cover as much as possible.Before you leave the bike?? On a Sunny day this may work as a greenhouse too and warm things up a little if the sun is in the right place.