I guess there's quite a number of Scarlatti thingies that could make people go wow for Baroque (like that one with lots of repeated notes Argerich plays on Youtube, can't remember the number)... As imbetter says, spending 3-5 minutes on that could work, as far as I can tell.
If you don't want to go Baroque, then you'll probably want something Classical. (Or, as I suppose you won't be allowed to use first-round selection for the second round - check that - use a Classical piece in the 2nd.) I've recently stumbled upon Beethoven's op. 22 and the first movement is very energic, lively and generaly smiley; it could prepare some nice ground for a more "serious" piece. Omitting the repeats, this would range five minutes.
If you play a lively Scarlatti or two in the first round, try something contrasting for the second piece - possibly one of the slow Chopin etudes, like 25-7. It can get rather hypnotic, if voiced well. Another thing of similar effect is the 2nd movement of the Schubert D960 sonata. We're roughly at ten minutes here.
Third piece - I'd go large-scale extravagant. I guess, knowing that you've done Gaspard, that recommending the first movement from Petroushka won't fall on deaf ears.

I don't know how much time you'll have to prepare, though; this would be a more long-term work. If you don't feel up to it, what about a Ligeti etude or two? Or some Shosty? (I'm not very familiar with his piano works, though...)
Second piece for second round - if you want a wild thing after the relatively composed (no pun intended) Beethoven, what about some Moussorgsky? If you make it short, then you could tranquilize the place a bit by Ravel's Une barque sur l'ocean.
Or, as an alternative round two programme, you could do Bach a minor P&F from Book I and Scriabin Vers la Flamme.
