How about allowing some head movement, by dragging the area outside inventory for example?

(sorry for the late response)
I've had this requested before in other places, I've been meaning to play around with some ideas to see if it's feasible but no promises how soon

I was about to propose that same feature :)

For an example of something that could be practical, check out elytraCameraMode in Tweakeroo, you set a hotkey (for example I use X), when the hotkey is pressed, you can control the head direction, when the hotkey is not pressed, mouse input passes through and does what it does normally.