Change line segment in graph

Question

How can I change only the first circle and the line that is connected to the other circle on a chart (line Chart)? I used the following code:

lines.lines[0].attr({'stroke-width': 8});  

The goal is to change the line width. But this changes the whole line, and I just want to change the first segment of it. This is possible?

Example: http://jsfiddle.net/aNJxf/20/