web api 2 - how to make api versioning more elegant

Question

What i want is something like the following code:

[VersionedRoute("api/user"), 1]
public class UserV1Controller : ApiController
{
    [HttpGet]
    [Route("aa")]
    public int GetVal()
    {
        return 111;
    }
}

[VersionedRoute("api/user"), 2]
public class UserV2Controller : ApiController
{
    [HttpGet]
    [Route("aa")]
    public int GetVal()
    {
        return 222;
    }
}

The key is I want the above code works just like Routeprefix with Route, they are so handy. I konw I can remove the "Route" attribute in the above code if there is only one method of each http verb, but it's not a good idea because I think in many cases we will use more methods in one controller. Now I have to write a lot of duplicated code using versionedRoute everywhere with a version number:

public class UserV1Controller : BasePublicController
{
    [HttpGet]
    [VersionedRoute("api/user/aa", 1)]
    public int GetVal()
    {
        return 111;
    }

    [HttpGet]
    [VersionedRoute("api/user/bb", 1)]
    public int GetInfo()
    {
        return 123;
    }
}

Is there any better implementation to version web api using custom header? Or how to upgrade the above code? There is a very similar question but I didn't find a better solution to my question.