RestSharp - How to send multipart/form-data body request without uploading a file?

I am unable to send a rest request using RestSharp where the body is encoded as multipart/form-data. How would you do this via RestSharp? Below is my current code:

string url = NDRoutes.Document;
        Boolean useXml = false;

        NewPaperDocumentRequest paperDocumentEntity = FillPaperDocumentRequest(createPaperDocumentRequest);
        RestRequest rr = _communicationsService.FormRequest(Method.POST, url, useXml);

        rr.AddHeader("Content-Type", "multipart/form-data");
        string body = JsonConvert.SerializeObject(paperDocumentEntity);
        rr.RequestFormat = DataFormat.Json;
        rr.AlwaysMultipartFormData = true;

        rr.AddParameter("action", paperDocumentEntity.Action, "multipart/form-data", ParameterType.GetOrPost);
        rr.AddParameter("name", paperDocumentEntity.Name, "multipart/form-data", ParameterType.GetOrPost);
        rr.AddParameter("extension", paperDocumentEntity.Extension, "multipart/form-data", ParameterType.GetOrPost);
        rr.AddParameter("cabinet", paperDocumentEntity.Cabinet, "multipart/form-data", ParameterType.GetOrPost);
        rr.AddParameter("failOnError", paperDocumentEntity.FailOnError, "multipart/form-data", ParameterType.GetOrPost);
        rr.AddParameter("return", paperDocumentEntity.Return, "multipart/form-data", ParameterType.GetOrPost);
        rr.AddBody(body);

        _communicationsService.ExecuteRequest(rr);