RC2 was released on October 2005, the first post on this thread that shows when I started this plugin is dated February 2006 and was based on the svn sources. So no QtWorkbench for the RC2 release, sorry...
P.S. Are you sure you could live with RC2 now that you know the features of the nightbuilds?
P.S.2 I am really busy these days (just returned from holidays so everything is just left behind at work waiting for my attention), so I haven't looked at the new API. I hope I have some free time to take a look at it.