I'd expect my writing style as an ethically unconstrained sociopathic AI to be sufficiently different from my regular writing style. But I also write fiction, so I'm used to trying to capture a specific character's "voice" rather than using my own. Having a thesaurus website handy might also help, or spend a week studying a foreign language's grammar and conversational style.
If you're especially paranoid, having a third party transcribe the log in their own words could also help, especially if you can review it and make sure most of the nuance is preserved. That really depends on how much the specific language you used was important, but should still at least capture a basic sense of the technique used...
Honestly, though, I have no clue how much information a trained style analyst can pull out of something.
Update 2013-09-05.
I have since played two more AI box experiments after this one, winning both.
Update 2013-12-30:
I have lost two more AI box experiments, and won two more. Current Record is 3 Wins, 3 Losses.