I have made a sample application to demo Play! framework 2.2, Spring data jpa and Backbonejs.
It is available at https://github.com/WarFox/play-spring-data-jpa-backbonejs.
Also a demo app is hosted in Heroku at http://play-spring-data-jpa-backbone.herokuapp.com/
It started as a fork from https://github.com/typesafehub/play-spring-data-jpa and then created a separated repo to include backbonjs.
Feel free to fork and play with it.