I'm pretty sure I've got a working implementation of what I wanted to achieve.
Using the attached source, the application gets netloaded into AutoCAD and registered for demandloading (props to
Kean for that)
then it's simply a case of typing "test" at the command prompt.
Excel will open and the Addin will display on the "TabAddIns" RibbonTab in the RibbonBar.
You then click "button1" and Excel returns control to AutoCAD.
What I need to do now is bolt on the tools created in
this thread and I'm done.