I tried to do this for a period that was not booked and was told that Airbnb could not create customized banners. I tried the suggestion of adding (for example) 20% discount 7/1-7/3 in the title of the site and then lowering the price on the listing for that period of time. I did try that and it attracted one guest. I wanted to have an offer that required staying for Friday through Monday or Tuesday of Memorial Day weekend and was told there was no way Airbnb could indicate that there would only be a discount for the whole stay.
It is important that hosts have more flexibility in making offers that work for them, resulting in more bookings for the hosts and savings for guests- as well as fees for Airbnb.