A tandem makes a nice base. It falls at a pretty constant speed and can hardly move around at all, giving the newbie a good idea of his own movements across the sky. A bit like the tunnel, only instead of bouncing off the walls, you can bump off the central reference point (or grab and hang on to it if you want to give the passenger an extra experience to remember).
Now all sarcasm aside, as a TI I also can't see why it would be a good idea to be chased repeatedly by someone who obviously can't fly his body well enough. I don't need to worry about another person in freefall and they have plenty of other ways to improve their skills.
As an aside, it also makes for a poor video, for the paying customer. The TI spends most of the time looking for the jumper and pays scant attention to his priority, the customer..............or is that just me???