There doesn't seem a way to submit a whole concept for a greeting card, not only the illustration with the thumbnails but add the text/content too as part of the submission.
AdminGagan Palrecha (Admin, Chirply) commented
This is a great suggestion, and I'll try to add it to our development plan soon! In the meantime, you can put the text part of the submission in the description area of the submission! Thanks for the suggestion!