Get an output different from input with elasticsearch completion suggester

I recently upgraded from Elasticsearch 1.4 to 5.4 and I'm struggling to migrate my autocomplete queries efficiently. The problem is that I want to have a completion suggester where the output is different from the input.

The documents I store have a field for categories which is basically an array of strings with their URIs (because they form a tree). The last part of the URI, I call it label, is the input in the completion suggester, but as a response I would like to retrieve the full URI.

So let's say I have two documents:

{
    "name" : "Lord of The Rings",
    "categories" : ["Books/Genre/Fantasy", "Books/Language/English"]
}

and

{
    "name" : "Game of Thrones",
    "categories" : ["Series/Genre/Fantasy", "Series/Host/HBO"]
}

My input is "Fant" and I want to get as a response the URIs for the "Series/Genre/Fantasy" and "Books/Genre/Fantasy" categories.

Previously with ES 1.4, I was able to create a completion suggester with a different output for a given input, so I indexed my suggesters like this:

{
    "suggest" : {
        "input": [ "Fantasy"],
        "output": "Series/Genre/Fantasy"
    }
}

and

{
    "suggest" : {
        "input": [ "Fantasy"],
        "output": "Books/Genre/Fantasy"
    }
}

But in ES 5.4, the output property doesn't exist anymore for completion suggesters so all I get in the response is the input property of my suggest field, which is the label "Fantasy", but I want the URI.

Right now, my workaround is to look for the categories field of each document returned in the _source property of the response, and filter on the categories that have a label starting with the input "Fant". It is very inefficient since I need to map every category of every returned document into its label to check with the input.

Isn't there a more efficient way to do that with ES suggesters? What am I missing?