web api 2 - how to make api versioning more elegant - asp.net-web-api2

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.