Dawntrail should give a Fantasia to all purchases.

[Reinha]

Put it on the first quest of Dawntrail as a reward would be how I would do it so no pre-order needed and people with multiple characters can fix changes to them via just doing the quest.

Since the graphics update also affects low level characters I think it would be more appropriate to mail it to every character with moogle mail like the previous account wide free fantasias.