You don’t so much commission Ralph Steadman as unleash him. The art direction is implicit in the decision to ask him for artwork. He is a force of nature. His acceptance of a commission is de facto an endorsement of a project – that adds value beyond even the illustration itself.
And I send my best wishes to the lame art director who tells him what, and how to draw. Actually no I don’t send best wishes. They would be foolish. But I may send flowers as commiseration.