Just pushed support for highlighting directly from source, without the need to store the fields as well: https://github.com/elasticsearch/elasticsearch/issues/issue/561.
And, a small enhancement to choosing fields to load. There is no longer a need to prefix with _source in order to load a field from the source document. If the requested field (or json sub substructure) is not mapped as stored, then it will automatically be extracted from the source. Here is the issue: https://github.com/elasticsearch/elasticsearch/issues/issue/562.