在WPF中使用自定义转换器时强制转换始终运行？

I'm implementing a custom date converter in WPF, the idea to be more clever about date entry, a la Outlook (being able to enter "today", etc.) So I've written my own converter, which is working. It formats the user's entry in the format M/d/yy. So for example, if they enter: 8-2, they'll see 8/2/09. Lovely. I'm implementing a custom date converter in WPF