You can have "primary" and "secondary" as action (method) names in the controller. Then you will need to add a new route (in class Application.WebApiConfig).
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}/{action}"
);
Or if "primary" and "secondary" are parameters to the same method. Then you might add this route
config.Routes.MapHttpRoute(
name: "DefaultApi",
routeTemplate: "api/{controller}/{id}/{priority}",
defaults: new { priority = RouteParameter.Optional }
);
In this case you will need to add an overload to your Get method that accepts two parameters (id, priority)
In both cases add the route before the main route, just in case to make sure it is the first one that has a match.