A way to customize iChat/Jabber status by buddy?

I use iChat and instead of setting a global status for everyone in your buddy list, is there a way to customize it so some people see you are available and some people don't?

I am wondering if this can be done through maybe an application or plug in, or some other way.

Additionally I use Jabber on iChat, and I am wondering if there is a way to appear offline while still seeing who is online?

thanks!