A pre-commit hook that checks if the corresponding review has been approved before let the commit proceed. 
The review number is obtained from the commit message as the number before REVIEW: keyword if, REVIEW: new is found a new review is created as the user doing the SVN commit.
With this hooks the clients doesn't need any program installed to post reviews as everything is done by the hook, simplifying a lot the setup of new contributers. 

Test in command line, eclipse, netbeans clients.
Working non stop for 3 months in a real deployment.