Calculate totals from highlighted cell in Excel file from ms access

I have an access query that I output to an excel spreadsheet.  When the excel file opens there is code in Access the does some formatting - bold text, auto size etc.

This is a report that shows all the vendor invoices.  The CFO would like to be able to highlight cells of the report yellow for the invoices he is thinking of paying.  So as he changes the cell yellow he would like to have a summary cell at the top that shows the amount going up as he highlights the cells.

He has to see what he can pay with current cash flow.

Didn't know the best way to do this.

I have tried to do the export from access to a .xtml template but could not get it to work - I don't think you can export to a template macro enabled.

I found some excel code that puts in a function formula in a module - when you highlight a cell yellow it will sum that cell.  So I thought about having code in access to create a new module with the function in excel.

Have not found a way to do this.

So not sure the best way to proceed?

Any suggestions?

Thanks,