Well, maybe a body paint artist would be the best bet. Looks like you've checked the curves route. If I remember correctly from my classes, a zone 2 grey will be the closest to white (zone 0) you'll be able to achieve while retianing the detail. I hope that you reach your desired effect, becuase if it's like the image you've posted, it'll be something to see. Oh, IMO, the image you posted is really nice. There's still seperation between the head scarf and the background.
I know that I am one with beauty, And that my comrades are one. Let our souls be mountains, Let our spirtis be stars, Let our hearts be worlds.