Oi eu estou fazendo upload de imagem no servidor php e carregado com sucesso com a ajuda deste código

- (NSString*)uploadData:(NSData *)data toURL:(NSString *)urlStr:(NSString *)_userID
{
    // File upload code adapted from http://www.cocoadev.com/index.pl?HTTPFileUpload
    // and http://www.cocoadev.com/index.pl?HTTPFileUploadSample
    NSMutableURLRequest *request = [[[NSMutableURLRequest alloc] init] autorelease];
    [request setURL:[NSURL URLWithString:urlStr]];
    [request setHTTPMethod:@"POST"];

//    NSString*  = [NSString stringWithString:@"0xKhTmLbOuNdArY"];
    NSString *stringBoundary = [NSString stringWithString:@"---------------------------14737809831466499882746641449"];
    NSString *contentType = [NSString stringWithFormat:@"multipart/form-data; boundary=%@",stringBoundary];
    [request addValue:contentType forHTTPHeaderField: @"Content-Type"];


    NSMutableData *body = [NSMutableData data];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]];
//  [body appendData:[[NSString stringWithFormat:@"userId=%@",_userID] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"userfile\"; filename=\"image%@.jpg\"\r\n", _userID] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[[NSString stringWithString:@"Content-Type: application/octet-stream\r\n\r\n"] dataUsingEncoding:NSUTF8StringEncoding]];
    [body appendData:[NSData dataWithData:data]];
    [body appendData:[[NSString stringWithFormat:@"\r\n--%@--\r\n",stringBoundary] dataUsingEncoding:NSUTF8StringEncoding]];
    // setting the body of the post to the reqeust
    [request setHTTPBody:body];

    // now lets make the connection to the web
    NSData *returnData = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];
    NSString *returnString = [[NSString alloc] initWithData:returnData encoding:NSUTF8StringEncoding];

    NSLog(@"%@",returnString);

    return returnString;

}

Agora eu quero enviar meu ID de usuário também no lado derver como posso enviar meu id de usuário? Eu tentei dessa maneira

[body appendData:[[NSString stringWithFormat:@"userId=%@",_userID] dataUsingEncoding:NSUTF8StringEncoding]];

mas em vão tentei enviá-lo desta forma

[body appendData:[[NSString stringWithFormat:@"Content-Disposition: form-data; name=\"userfile\"; filename=\"image%@.jpg\"; userId=\"%@\"\r\n", _userID, _userID] dataUsingEncoding:NSUTF8StringEncoding]];

mas novamente em vão tão gentilmente me guiar o que fazer!