At the moment the C'tis taskmaster is worse than indie commanders, but costs an extra ten gold. My suggestion is giving them a 'Capture slaves' command, similar to Mictlan's tribal kings, but creating (fewer) lizard slave warriors.
Of course, modding tools to allow this sort of thing would be great as well .
Supposedly, they're the only who can control the slave lizards, so I guess they should have something linking them to slave lizards. I agree with quantum
Actually we had something like that in mind when we developed Dom 1. Unfortunately we ended up with several dozens of commander types and it made leadership and micromanagement of armies a big bother. We had started to include leadership types for lizards, abysians, jotuns, knights (knights do not like to take orders from those not noble-born) etc.
Some kind of restriction with lizars slaves might be good though. The taskmaster is not very useful as it is.