RethrowException.cs

// NOTE: this method does not throw it just "prepares to be thrown"
static Exception Rethrow(this Exception ex)
{
    try
    {
        typeof(Exception)
            .GetMethod("PrepForRemoting", BindingFlags.NonPublic | BindingFlags.Instance)
            .Invoke(ex, new object[0]);
    }
    catch (Exception) 
    {
        // this method is about preparing exception to be thrown
        // so if it throws exception we just don't care and return
        // original exception
    }
    return ex;
}

// NOTE: this method does throw
static T Rethrow<T>(this T exception)
    where T: Exception
{
    ExceptionDispatchInfo.Capture(exception).Throw();
    // it never actually gets returned, but allows to do some syntactic trick sometimes
    return exception; 
}