Dear Raivo,
I think you are onto something very important here. In my reading of the suttas sense restraint is more about wisdom than will power. Will power, as you suggest, can only be maintained for so long, and it is a bit painful at the same time. Wisdom is seeing things clearly and as such the mind just turns away by itself, and very little will power is required. Please have a look at MN19. It seems to me that this sutta is saying precisely that wisdom is the way to overcome the defilements. AN2:11-13 too are interesting in this regard.
With metta.