The EGU journals work this way. Official reviewers are assigned, but third parties can comment. An example submission http://www.the-cryosphere-discuss.net/5/1

The EGU journals work this way. Official reviewers are assigned, but third parties can comment. An example submission http://www.the-cryosphere-discuss.net/5/1749/2011/tcd-5-1749-2011-discussion.html http://www.the-cryosphere-discuss.net/5/1749/2011/tcd-5-1749...