The possible reason for a region restriction could be a pending deal with, let's say, a European distributor who wants to show the doc in theatres or wants to release a dvd/bluray.
Anyway, you could use a VPN Tunneling service like Tunnelbear to access the movie. Super easy app for pc/mac. It's free for the first 500mb. Activate it, buy or rent the movie and than disable or uninstall tunnelbear.
Once you have bought the movie, you can watch/stream it from any location in the world