I think it would be possible on New Game difficulty and surely it has already been attempted before. It would definitely get progressively more tedious on higher difficulties, and the shooting range rewards would have to be skipped altogether, as buffing for later levels (like 5) is mandatory. Tedious, since you deal less damage and have less resources, hence why ideally you compensate with PE. I don't take suggestions, but I do consider commissions. If there's a person willing to fund a walkthrough of exquisite quality, I would be up for an attempt.