You should be able to add additional controllers that are ignored by CMS. For instance in your global.asax.cs:

protected override void RegisterRoutes(RouteCollection routes)
{
    base.RegisterRoutes(routes);

    routes.MapRoute("AdditionalDiagnosticRoutes", 
                    "diag/{controller}/{action}/{param}", 
                    new { action = "Index", param = RouteParameter.Optional });

}

I added some additional diagnostic controllers that are not part of the CMS page/block controllers.

And controller itself:

public class VersionController : Controller
{
    [Authorize(Roles = "CmsAdmins")]
    public ContentResult Index(string assemblyName)
    {
        var fvi = FileVersionInfo.GetVersionInfo(Assembly.GetExecutingAssembly().Location);
        var version = fvi.FileVersion;

        return new ContentResult { Content = "Current version: " + version };
    }
}

You would need to prefix Html.ActionLink to point to your controller's url.