I had OSX with Java 1.6 installed, and I just installed jenv along with Java 1.7:
Java 1.6
jenv
Java 1.7
$ jenv local \'1.7\' $ jenv versions s
Now, there's a new option how to set JAVA_HOME via jenv export plugin:
jenv enable-plugin export
See https://github.com/gcuisinier/jenv/issues/44#issuecomment-233124185