You can set the CustomDraw property of individual links. If you cannot decide whether a link should be custom drawn until the event is raised, you can draw its segments easily by calling the DrawLines or DrawBeziers method of e.Graphics with ControlPoints.GetArray() as argument, and calling link.DrawArrowhead to draw the arrowhead shapes. That won't work if you use the LinkCrossings property though.

Alternatively, your DrawLink handler could do something like this to run the standard drawing code:

e.Link.CustomDraw = None;
e.Link.Draw(e.Graphics, new RenderOptions());
e.Link.CustomDraw = Full; 

I hope that helps,
Stoyan