Using a larger pulley would reduce boost across the range, so it would make it harder to turn at low speeds. I don't know how the pump works, but my guess is that at road speed you would be running the pump fast enough to have full boost, so it might not improve feel at all.
I think you would have better results with a variable ratio steering box, or a way to vary pump pressure. Variable ratio boxes are not that unusual, but there may not be one for your vehicle. One of the Honda's I had several years ago used a mechanical speed sensor in the PS pump line, and it reduced the steering boost as soon as you went above a certain road speed. You could turn the wheel with your pinky at idle, but it retained very good feel at road speed.