I don't think there's an easy way for doing such a thing.
But I'd read Jdbc input plugin | Logstash Reference [7.12] | Elastic
That's being said, I shared most of my thoughts there: http://david.pilato.fr/blog/2015/05/09/advanced-search-for-your-legacy-application/
Basically, I'd recommend modifying the application layer if possible and send data to elasticsearch in the same "transaction" as you are sending your data to the database instead of trying to read that later and try to compose complex objects (this has a significant cost on the source database).
Have also a look at this "live coding" recording.