You can either use custom drawing or attached nodes to implement this.

Custom drawing can be done by deriving from the DiagramLink class and overriding its Draw method, or by setting the CustomDraw property and handling the DrawLink event. Then you can use the DrawingContext methods to render the arrow and labels.

The other option is to use the AttachTo method to attach three auxiliary nodes to the link so that they display the labels and menu arrow. You can also combine this with a LinkModifying handler that distributes the attached nodes uniformly along the horizontal link segment.

I hope that helps,
Stoyan