Show modal view controller with custom frame in iPad

I want to show a modal UIViewController with a custom frame in iPad, centered on top of its parent view controller.

I tried using a form sheet but as far I know the frame and shadow effect can't be changed.

vc.modalPresentationStyle = UIModalPresentationFormSheet;
[self presentModalViewController:cv animated:YES];

I also tried using a popover but as far as I know either I can't center it or I can't hide the arrow.

Is there another way to show modal view controllers? Is it possible to solve this problem by using form sheets or popovers?