I would like to have a custom menu (CommandBarPopup) to have it's items
enabled/disabled depending on the current user selection (e.g. chart/cell).

The problem I'm facing now is that there is no Click property attached to
the CommandBarPopup class. I am aware of the OnAction property which can be
used to call VBA code, but what is the best way to approach this?

This is for a COM Add-in, not for a single workbook and all the examples
I've seen of using VBA are bound to a single file.

The rest of my Add-in is written in C#.

I was considering having a placeholding CommandBarButton that, when Clicked,
would execute the required code, before making itself invisible and making
the true CommandBarPopup menu visible.

However, this solution is for blind users, who would be accessing the menu
via keyboard shortcuts and having the contents read out by a screen reader.
If the menu item originally selected is not the CommandBarPopup, I don't know
how this would confuse the screen readers/users mental model of what is going
on.

So, in short, how does one invoke a method upon the clicking of a
CommandBarPopup?