Aggregation in another scope with dynamic value

Mapping.json

{
    "_id" : {
        "store" : true,
        "index" : "not_analyzed"
    },
    "_timestamp" : {
        "enabled" : true,
        "store" : true
    },
    "properties" : {
        "processDefinition.id" : {
            "type" : "string",
            "index" : "not_analyzed",
            "doc_values" : true
        },
        "processDefinition.key" : {
            "type" : "string",
            "index" : "not_analyzed",
            "doc_values" : true
        },
        "processDefinition.name" : {
            "type" : "string"
        },
        ...
        "variables" : {
            "type" : "nested",
            "properties" : {
                ...
                "name" : {
                    "type" : "string",
                    "index" : "not_analyzed",
                    "doc_values" : true
                },
                "rawValue" : {
                    "type" : "string",
                    "index" : "not_analyzed",
                    "doc_values" : true
                }
            }
        }
    }
}