Thanks to my HR Systems Team for this next trick.
If you only have one vacancy template that you use and you want it to be the auto-picked template without needing to go through a configuration option and further activity profile work, you can achieve this as follows.
Create the vacancy template and ensure at least 1 data item is set (we manually added an opportunity called ‘Select a College/Service...’ that has order ‘1’ for a department local lookup list opportunity item so it appears right at the top of the list.
After the form has been saved, we added a bogus ‘DEFAULT USER’ account that isn’t by anyone as a Participant.
That’s it :)

