Apologies for the delay! You can post treats to the AO3 community by going here, clicking "Post to Collection" toward the top right, and then manually adding the recipient's AO3 username in the field that says "Gift this work to".

Your work will then go into the collection and be revealed with the rest of the gifts when the collection opens (and your name as the creator will be revealed when the other creators are revealed, a week after the collection opens).

Hopefully that makes sense! If there's anything else, just ask.