When I took Rod Jenkin's class I believe he told us, or intimated, that about 9 out of 10 people can achieve a release using the method Arne describes. Unfortunately, the 10th person continues to increase back tension until they become blue in the face, but the release doesn't happen. I've found this to be true in my own classes.
If you are this unlucky 10th person, then the best advice is to simply relax your string hand at the appropriate moment and the arrow will go off. Don't try to open your string hand, just relax the fingers and let the string push them out of the way.
Be careful about decreasing any finger tension prior to release; it is easy for this to devolve into a collapse. You'll know if you do this, because you'll probably pluck the shot.