Hi Jeff,
Unfortunately this is a gap in our function set for GRAPH objects. I have been told by the developers that there is no VBScript-level function to create a Y axis programmatically. Your only option as far as I know is to have several copies of the same report layout saved off with different numbers of Y axes. As you accurately pointed out, once the Y axis exists, you can programmatically associate various curves with it or edit its properties.
Sorry for the bad news,
Brad Turpin
DIAdem Product Support Engineer
National Instruments