I think as of now Giovinco is best suited to be a supersub. It seems he gets frustrated as time goes on and his performance drops. Throwing him on for the last 20-25mins seems to be where he is the most effective.
I'd start Vucinic - Quagliarella against the Danes. Throw on Gio, take off a wingback and switch to a 4-3-3 to confuse the opposing side during the later stage of the match.