Often flying schools will offer a 'waiver' for lets say $5 an hour. If you pay it they promise not to come after you for the excess/deductable and will claim the balance from their insurance. It's not an insurance policy per se, but acts like one as far as the client is concerned. If only covers you for the hull loss, you are not covered if you cause damage to a third party in the same way an avemco policy would.
If there is a insurance policy available by the hour which covers third party liability then I have not heard of it. This thread has certainly become a bit messy.