You can use a vignette that's extremely subtle, not really "visible" per se. If you want to draw attention somewhere, and you don't want to be obvious about it, use a combination of subtly applied methods.
That's why I suggested a vignette, together with an increase in local contrast. The vignette pushes the eye, unconsciously, toward the middle "nothing to see out here" and a slightly crunchy sharpened/contrasty look on the back of the dress draws the eye inwards "hmm, something to look at here" all without being obvious. The viewer simply finds their eyes looking at the right thing.