Hi misticmerlin,
Yes, you can do it with Excel, but I see no reason why you can't do it with a simple text file with your selections. Yes, you would have to specify names instead of indexes, but beware that BetFair may change the order of horses in a race at any time, so this would be inefficient anyway.
You just create a text file, add all your horses there, press the "Import selections for auto-trading" button and specify the file path.
The program will then disable all selections except the ones you've added.
Then add a Dutch back trigger with a desired amount to win, and the job is done.