Hi Peter,
Just came across this post of yours from earlier this year. Have you found a solution for this yet? If so, could you post the empty file here?
I'm not well-versed with VBA but am good with Javascript and Python, have done this for some data in python.
I'm toying with an idea for making a website that does this conversion for you : You copy-paste your data in from your table, and get a plus code column added. I'd do it in javascript so that the operation would be wholly at client side and people can save the page and use if offline and not have to give their data to anyone. I'll make this faster if there is a real world need, so let me know!
-Nikhil VJ
Pune, India