If you can't quite get it with your hands, you can slip a pipe over each brake arm and pull apart (try to put it in a vise first).  You'd be surprised, but a lot of shops actually use this technique.  Be careful not to crack the plastic pieces near the heel, though.  If it still doesn't work, you can buy just the wide brake for pretty cheap and you are still ahead since the bindings were a steal.  Good Luck!