Associate document with a pre-existing child


Is it possible to specify an already existing object as a nested
(child) object of a newly indexed one? I have a small number of
persons that are associated with a big number of things. I'm doing
most of the searching on things, so I need to be able to fetch those;
if I nest things in persons, then I wouldn't be able to do that.
However, in some cases I need to search for things via the persons
they belong to, and I'd like to avoid indexing the same person
thousands of times (because then editing the person becomes a
consistency nightmare). Using IDs is out, too, because I may have to
search for persons by name and date of birth. Is it possible to tell
ElasticSearch to use a pre-existing person object as the nested child
of a thing object that i'm adding to the index?