Create a custom UIButton with a custom background image and stretchable width.

UIStretchedButton.m

// 1. Create a PNG background image.
// 2. Use UIEdgeInsets to stretch the image eg. 8.0f left and right of rect to remain unstretched
// 3. Make sure the UIButton height is the same as the image height

UIImage *image = [UIImage imageNamed:@"button_background_blue.png"];
UIEdgeInsets insets = UIEdgeInsetsMake(0.0f, 8.0f, 0.0f, 8.0f);
UIImage *stretchedImage = [image resizableImageWithCapInsets:insets];

[self.button setBackgroundImage:stretchedImage forState:UIControlStateNormal];