UINavigationControllerを遷移済みの状態で開く方法

以下のようにself.addChildViewController()を複数回実行すると、
FirstViewControllerからSecondViewControllerに遷移した状態になります。
(FirstViewControllerへは、self.navigationController?.popViewControllerAnimated(true)  で戻ることができます。)

import Foundation
import UIKit

class NavigationController:UINavigationController {
    required init?(coder: NSCoder) {
        super.init(coder: coder)

        let firstViewController = FirstViewController()
        self.addChildViewController(firstViewController)
        let secondViewController = SecondViewController()
        self.addChildViewController(secondViewController)

    }

}
import Foundation
import UIKit
class FirstViewController: UIViewController {
    〜略〜
}
import Foundation
import UIKit

class SecondViewController:UIViewController{

    var leftBarButton: UIBarButtonItem!

    override func viewDidLoad() {

        leftBarButton = UIBarButtonItem(title: "< Previous Page", style: .Plain, target: self, action: "tappedLeftBarButton")

        self.navigationItem.leftBarButtonItem = leftBarButton
    }

    func tappedLeftBarButton() {
        self.navigationController?.popViewControllerAnimated(true)
    }
    〜略〜
}