[Phoenix-D]

If you could adjust the AI files, you could do what SJ suggested and make them fighters. They'd show up as blue radar dots though (red when you shot them), which might or might not be a good thing. What I'd do is make a new 'race' and add some of the asteroids to it. So you have the big, immobile ones and some smaller moving ones.

As a bonus, make special components for them and they'd occasionally drop a cargo container. You could make the component useless, so the player would be forced to sell it..