Make default selection a custom form setting, not a custom field setting

We would like the default selection for a field to be a custom form setting and not a custom field setting, just like required field logic works. For example, we have a "Region" field that we use across many different custom forms for reporting purposes. If that Region field is used on a form that is specifically for Northern Europe, we would like to have the selection default to "Northern Europe" only on that particular form, not across all forms.