public class WebApiApplication : System.Web.HttpApplication
{
    protected void Application_Start()
    {
        CheckAddBinPath();
        GlobalConfiguration.Configure(WebApiConfig.Register);
    }

    public static void CheckAddBinPath()
    {
        // find path to 'bin' folder
        var binPath = Path.Combine(new string[] { AppDomain.CurrentDomain.BaseDirectory, "bin" });
        // get current search path from environment
        var path = Environment.GetEnvironmentVariable("PATH") ?? "";

        // add 'bin' folder to search path if not already present
        if (!path.Split(Path.PathSeparator).Contains(binPath, StringComparer.CurrentCultureIgnoreCase))
        {
            path = string.Join(Path.PathSeparator.ToString(), new string[] { path, binPath });
            Environment.SetEnvironmentVariable("PATH", path);
        }
    }
}