set a button's background image in interface builder then stretch it in code

gistfile1.m

- (void)awakeFromNib
{
    [self strechImageForControlState:UIControlStateNormal];
    [self strechImageForControlState:UIControlStateDisabled];
    [self strechImageForControlState:UIControlStateHighlighted];
    [self strechImageForControlState:UIControlStateSelected];
}

- (void)strechImageForControlState:(UIControlState)controlState
{
    UIEdgeInsets insets = UIEdgeInsetsMake(25.0, 25.0, 25.0, 25.0);

    UIImage *image = [self backgroundImageForState:controlState];

    //these are just example insets, I'm not sure if they're correct
    image = [image resizableImageWithCapInsets:insets resizingMode:UIImageResizingModeStretch];

    [self setBackgroundImage:image forState:controlState];
}