It's really difficult with the AI. They fly a strange jinking pattern where they drift off course by as much as 5 to 10 degrees then jerk back. This of course makes keeping with them a pain.
There's also the fact that the AI fly at a high cruise speed which makes getting near them hard unless you have a much faster airplane and that creates problems because then you have to slow down almost to a stall for the faster airplane to keep up with the AI at cruising speed. Haven't tried it online with anyone but that would probably be a lot easier.
Now just buzzing the AI is a lot less difficult and a lot of fun to boot. Just take up a jet and chase the Cessnas and Pipers around a little.

See how close you can come without crashing (hint: not too close because Fs9 uses bounding box detection for air to air crashes).