How do you set stretchableImageWithLeftCapWidth in Interface builder?

How do you set stretchableImageWithLeftCapWidth in Interface builder?

From stackoverflow

• Interface builder does not support stretchable images.

  -(void) viewDidLoad {
    [super viewDidLoad];
    [myImageView setImage:[[myImageView image] stretchableImageWithLeftCapWidth:5 topCapHeight:5 ]];
  }