Is it possible to add a driver to a vertex position? I want to add a driver to a vertex' z position. Is this possible? If it is, how?

When I try to add a driver, all I get is the option to edit source and edit translation.
In edit mode, select the vertex you want to animate. Then CtrlH > H (Hook to new object). This will create an empty, whose position you can animate, and the selected vertex will follow it.