I do not have any experience in setting up a concerned relatives/ex-members group, I do have experience in my own recovery from destructive groups.
The Rick Ross site has excellent information, including links to support groups from [www.culteducation.com
The Cult Education Forum has helpful thoughtful information also. You could possibly start a thread themed on this particular church, encourage others to join in.
You could set up a Yahoo or Usenet group to discuss the church. You could set up your own web page and host a forum there.
You could check with various organizations and support folks and see what resources they have to offer.
You could start with others a reading group, read through books on cults, thought control, recovery, legal matters etc. Could expand the reading group to include guest lectures from people in the cult recovery field and related themes.
It is admirable that you want to do such work, I'd suggest you make sure you take good care of yourself also.