Well, you can do it manually. Your best time is, as you said, in the results file. The AI laptimes are in the XML. All you have to do is compare the two to figure out whether the AI needs a nudge up or down. Personally, I've got a pretty good idea of what level I'm at so by now I can 'program' the AI pretty quickly. Start at the approx. AI level and then run a series of one-lap races until it starts to outrun you. And that's it.