$ curl -XPOST localhost:9200/test -d '{"mappings": {"BOOSTER": {"properties": {"boostable_str": { "type": "string", "index": "not_analyzed", "omit_norms": "false" }}}}}'
{"ok":true,"acknowledged":true}

$ curl -XPUT localhost:9200/test/BOOSTER/DOC-1 -d '{ "boostable_str": {"_value": "boosty string", "_boost": 5}}'
{"error":"MapperParsingException[failed to parse [boostable_str]]; nested: IllegalArgumentException[You cannot set an index-time boost on an unindexed field, or one that omits norms]; ","status":400}

$ curl -XGET localhost:9200/test/BOOSTER/_mapping?pretty=Y
{
  "BOOSTER" : {
    "properties" : {
      "boostable_str" : {
        "type" : "string",
        "index" : "not_analyzed",
        "omit_norms" : true,
        "index_options" : "docs"
      }
    }
  }
}

$ curl -XGET localhost:9200/test/BOOSTER/DOC-1?pretty=Y
{
  "_index" : "test",
  "_type" : "BOOSTER",
  "_id" : "DOC-1",
  "exists" : false
}