Create a macro  inside the add-in with this single line of code.

ThisWorkbook.IsAddin = False

I would also suggest creating one that reverse this . . .

ThisWorkbook.IsAddin = true

Assign each to a separate toolbar button and you should be set.

I do have a
followup. Excel thinks it has to save the add-in after I do some
work and on exit asks to save the file. If it gets saved by the user
and the property is set to false, the addin  will be corrupt. Is there
a way to prevent the message?

I did resolve this by setting a workbook property "saved" to true.
Thanks for the help.