This Dark Souls 2 mod (via RockPaperShotgun) involves tricking the zoom on the bow or binoculars. The effect is a surprisingly robust first-person view that actually doesn't look hacked at all. Even more surprisingly in this video, YouTuber Benzoin-Gum makes it look playable. Although, I suspect he's had plenty of practice.
You'll need to download this file and Cheat Engine to run the mod (the latter meaning there's a risk of being banned if you go online). To 'set' the first-person mode you'll have to freeze the camera zoom value, equip a bow or binoculars, and then zoom in. The view will stay there, creating the FPS camera effect.
It's a bit temperamental: cutscenes and loading will reset the view, movement is not completely aligned with the camera and there's clipping because the game obviously doesn't know where the hell you are.