Bounce Dryer Sheets for back window shrink, 120 Count
A dryer sheet heat shrink!
spray some water on the outside and wipe a dryer sheet all around so that it deposits the fabric softener onto the window. Let it dry and it will leave a residue. Now lay your film over, cut oversize, and anchor horizontally as if you were doing a normal dry shrink, but DO NOT use water under the anchor, you won't need it, the film will now stick to the glass when smoothed as if it were wet.
The beauty of this method is accuracy in the distribution of shrink, no need for follow-up wet shrink.