You know what would be awesome, satisfying, likely to occupy Riddles thoughts and totally not morally objectionable?
Spiking Lockhart's drink with truth potion.
We might make him spill the beans in front of professors, thus publicly embarrassing him and causing him to get fired.
Or do it in his class, prompting him to memory wipe whole class of children (some of them noble) and then pointing discrepancy in her memories to Ginny to make her to go straight to Dumbledore, who will proceed to send his quack ass to Azkaban.
And how do we get our hands on truth potion in first year? Please. We're a sibling of Fred and George.