What is the policy for the posting of art gifts on tumblr?

I'm making an art gift for one of the wishlists, but I only use my AO3 account for fanfic, so I don't want to post it there. I'd like to post it to tumblr, but tumblr has no way to hide a post (afaik).

So do I just respond to the wishlist in question with a "gift will be linked to soon" message and then post on tumblr and drop the link in another comment on the wishlist once reveals day comes around?