Sync custom idea fields to native feature fields

While we know how to sync custom field across ideas and features, there are some cases where we collect information in Ideas that should be synced to a native feature field. There does not appear to be a way to connect them. Naming the custom field with the same API value as the native field (per instructions for connecting two custom fields) does not seem to have any effect.

For example, we collect a "need by" date in a custom date field on Ideas that we want to sync to the native "due date" for a feature. 

A solution using newly released automation functionality to populate a field on a record FROM a value on a related record could also work. Automations to update fields appear to be fairly limited especially for date-related fields.