Steve,
If you have access to the backside, and if you have a good selection of dollies (or you're willing to grind a dolly to contour), and if you intend to polish.....
Shrinking and stretching are not that hard. Everything revolves around understanding a basic concept. To stretch, you hit "on-dolly". To shrink, you hit "off-dolly". Not hard to tell the difference; if the dolly rings when you bump, you're on-dolly. If the bump sounds dead, you're off-dolly.
From there it is pretty much a question of selecting the right tools to fit the physical situation. The shape of the part and the degree of access to both sides are the wild cards. In this case the dolly must match the contour very closely. I'd probably use a slapper rather than a hammer.
Soft material (1100, 3003, 5052-0) works easily. Tempered 2024-T3 material makes this job much more difficult. You can use heat with non-structural aluminum parts, but that's not the case here.
If you choose to pursue the matter further, do not work this skin any further until you play with some scrap, same material, same thickness. Knock a similar dent in the scrap and practice.
Having said all that, if you're going to paint the airplane just take a round face hammer and knock it back to an "in" dent, then fill it before you paint.