Okay. It doesn't seem like I can get the system to trust commenters unless they're logged in somehow. So after some tinkering I've managed to get TypeKey authentication to work. You can login using your LiveJournal ID, if you have one. Then I have the system trust you, and then your comments will be posted automatically. TypeKey, LiveJournal, and Moveable Type are all made by a company called SixApart, which is why they work so magically well together.