Adding a simple vertex to a freeform line

[MarkJ]

Having created a freeform line I wish to add an additional ordinary vertex to
the line.
The only way I know of adding a vertex is <CTRL> left mouse button. This
adds a spline type vertex with adjustment handles .
I would like to add plain vertexes, the same type as the initial freeform
line already has.
Does anyone know how?

(I am using VISIO 2000)