Spring MVC Controller: display automatically set up Thymeleaf error page without throwing Exception

Question

I have an auto configure Spring Boot error page setup, as described in this answer. Currently I trigger the showing of error pages by throwing an exception, which works fine. But I'd like to not use Exceptions for control flow, so I'm looking for an alternative way. I also don't like that I have to create a new Exception, which is costly.

@GetMapping("/user/{id}")
public String showUser(@PathVariable Long id, Model model) {
    Optional<Long> idOptional = userRepository.findOne(id);
    if (idOptional.isEmpty()) {
        throw new ResponseStatusException(HttpStatus.NOT_FOUND);
    }
    // do stuff
    return "user/index";
}

I know I can use the HttpServletResponse to set the status but then I bypass the Spring Boot error page handling and have to render the template myself, so I have to add the model attributes myself:

@GetMapping("/user/{id}")
public String showUser(@PathVariable Long id, Model model, HttpServletResponse response) {
    Optional<Long> idOptional = userRepository.findOne(id);
    if (idOptional.isEmpty()) {
        response.setStatus(404);
        model.addAttribute("status", 404);
        return "error";
    }
    // do stuff
    return "user/index";
}

Is there a way of to use the custom error page support (not specifying and preparing the template myself) without throwing an Exception?