Stu,
Right now there are not Eclipse Release Candidate Software packs. The new Eclipse 4.2.2 SDC Software pack will be release nearly the same date as Eclipse.org release Eclipse 4.2.2 . Eclipse 4.2.2 was scheduled for last Friday but it got a delay, for more information http://www.eclipse.org/forums/index.php/m/1013445/
As a workaround you could add as third-party library the 4.2.2 update site, and Juno SR2.
Best Regards
Ignacio
SDC Support