Hi @awc
This is exactly what I have advised previously:
It may be possible to customize the select2 JS args and allow a custom value to be saved, however, you will then need to append this value to the options page (I’m assuming you have a textarea field with all user choices)?
Checkout the JS customization here:
http://www.advancedcustomfields.com/resources/adding-custom-javascript-fields/
You could use the filter acf/update_value to get the select field’s value, and if this value does not exist within the options page textarea, you could add it using the update_field() function.
This will take quite a lot of customization, trial and error, debugging. I don’t have a working example of this, but almost anything is possible with code
