有什么方法可以让WPF textblock可选?

I want to make the text displayed in the Witty, an open source Twitter client, selectable. It is currently displayed using a custom textblock. I need to use a TextBlock because I'm working with the textblock's inlines to display and format the @username and links as hyperlinks. A frequent request is to be able to copy-paste the text. In order to do that I need to make the TextBlock selectable.,