Hello @TomD
Welcome to the Forum 
Unfortunately @JMichaelTX will not reply to you in any of his threads on this Forum - I am very sorry to say that... he is missing here
Go to The Passing of JMichealTX to get more information on that.
Here is another Example Macro from Jim which should give you an idea on how to accomplish your task.
Dynamic Default List for Prompt For User Input [Example]
Greetings from Germany
Tobias