gistfile1.m

// Assuming property UIPageViewController *pager.

- (void)viewDidLoad
{
    [super viewDidLoad];

    // Create it.
    self.pager = [[UIPageViewController alloc] initWithTransitionStyle:UIPageViewControllerTransitionStyleScroll navigationOrientation:UIPageViewControllerNavigationOrientationHorizontal options:nil];

    // Point the datasource back to this UIViewController.
    self.pager.dataSource = self;

    // Start at the first page of the array?
    int initialIndex = 0;

    // Assuming you have a SomePageViewController which extends UIViewController so you can do custom things.
    SomePageViewController *initialViewController = (SomePageViewController *)[self viewControllerAtIndex:initialIndex];
    NSArray *initialViewControllers = [NSArray arrayWithObject:initialViewController];
    
    // animated:NO is important so the view just pops into existence.
    // direction: doesn't matter because it's not animating in.
    [self.pager setViewControllers:initialViewControllers direction:UIPageViewControllerNavigationDirectionForward animated:NO completion:nil];

    // Tell the child view to get ready
    [self.pager willMoveToParentViewController:self];

    // Actually add the child view controller
    [self addChildViewController:self.pager];

    // Don't forget to add the new root view to the current view hierarchy!
    [self.view addSubview:self.pager.view];

    // And make sure to activate!
    [self.pager didMoveToParentViewController:self];
}