A quick housekeeping note: I’ve moved this to a new topic since the original topic is quite a bit old and replies on it alert all of the previous participants.
I’m led to believe the answer is “no” based on a bit of poking around on the Trello web client. Unless I’m missing something, using the Trello web client, you can’t create a card with a cover–you can only add a cover after the card is created.