Arksly- I also bent a hoof pick backwards trying to remove ice balls!
When I had that problem, I would just take a cheap, sturdy hoofpick (like from Princess Auto) and get it under the ice in the grooves of the hoof, if I could, and pop the ice out in one piece. If I couldn't get it off that way, I would just try to chip away at the edges until I could get the pick under, or get it off bit by bit. I've never been fortunate enough to board anywhere with a barn, never mind warm water!
They seem to be so much stronger and you don't have to worry about breaking it!