I'm not a controller user so I might not tell you the best way but as a controller the only way I can guess is to have the standard cam (the character needs to follow the camera) and look with the camera on the opposite side of the target. At this point when u cast a spell just spam right left (cam) to overwrite the autofacing frames and go back to looking where the camera is pointing.
Id also like to point out that actually the completely opposite camera does not work with wide hitbox targets or when you are far from target, but you should aim the cam at approximately perpendicular (~90°).
Then by doing a few tries on the dummy you understand more or less where the camera should point so as not to make the cast fail.