Basically, you need to add another Geometry section to the ShapeSheet. This section is for your line to control point.
The new geometry section needs two entries, beginning point (1st line) & ending point (2nd line).
First line is a MoveTo:
X Cell: enter the x position of the control point, something like Controls.Row_1.x.
Y Cell: enter some point on the shape, e.g., height*1
2nd line is a LineTo:
X Cell: same entry as above
Y Cell: is the Control point y position, e.g., Controls.Row_1.y.
That's it.
HTH
Wapperdude