Answer
No — per IFS R&D, this is a genuine technical limitation of the Custom Object Framework, not a missing configuration option. Reference-type custom field values are stored internally as a rowkey rather than as the display text you see, so there's no way to support typing against them — the display value is resolved from the rowkey, but the field itself doesn't hold that text. Because of this, reference-type custom fields can only be populated through their LOV; there's no way to enable free-text entry for this specific field type. If free typing is a hard requirement, using a plain Text-type persistent field with separate validation logic instead of a Reference-type field is the usual workaround, accepting the tradeoffs of a different field type.