Indeed, you could try giving them an assignment that involved complex ideas, ideas that no one thought Alice could do (on its own;without scripts or modifications) when first seeing it. I don't mean things that often come up such as FPSes, but perhaps Street Fighter or
complex code based spells such as in Warcraft III. Trigger/JASS based spells in Warcraft III were probably the most spectacular player-made things you'd ever seen, and believe it or not they are completely possible in Alice, give or take a few nonexistent models.