There are times when I get a job that requires removal of some old film that seems impossible to get off on commercial glass. Here's how I make it a little easier...

I take my 6" triumph and shove it on the end of a broom stick and go to town on the old film. You get much better leverage this way.

I know the risk of breaking the glass maybe higher, but Ive yet to break one and it makes removal a cake walk.