I think you're referring to the fact that Poser itself won't add ERC to anything but the body, and it will only add morph controls.

As long as you do it by hand, you can have the master ERC dials in any body part, and they can control any type of dial you want. If you look in one of the Poser 6/7 figures' CR2, you'll see that the head controls eye rotation using ERC.

I recommend CR2Builder for Poser file editing.