Hi Yael,

There's no property for this on the control, but you can do it using a CreationFilter, and it's a pretty simple one.

    public class MyUltraOptionSetCreationFilter : IUIElementCreationFilter
    {
        #region IUIElementCreationFilter Members

        void IUIElementCreationFilter.AfterCreateChildElements(UIElement parent)
        {
            // Do nothing
        }

        bool IUIElementCreationFilter.BeforeCreateChildElements(UIElement parent)
        {
            OptionSetOptionButtonUIElement optionSetOptionButtonUIElement = parent as OptionSetOptionButtonUIElement;
            if (optionSetOptionButtonUIElement != null)
            {
                optionSetOptionButtonUIElement.CheckAlign = ContentAlignment.MiddleRight;
            }
                        
            return false;
        }

        #endregion
    }