This took me a while to find so I'm adding it here.
I was trying to use the
Project From View
UV Unwrap and because 1. there's no way to roll the view camera and 2. the camera gimbal locks at the poles I was having a lot of trouble getting the correct direction to match my texture.
The answer is of course to put the camera in quaternion mode, but I had no idea how to achieve this. There's the
Transform Orientation selection box which has the
Gimbal option but this is not for the camera's transform.