Your exact scenario is already available in our current offering.
This is achieved through 'Content Items' section in the admin. Structured content is the idea of banner ads and content that a user sees. You can create rules for when this structured content shows up (the 'where' currently is done in the template code):
If you instantiated a private demo (http://www.broadleafcommerce.com/demo
) then you can go into the admin and play with some of the content items in there. The big banner on the home page is the 'Shirt Special - 20% off all shirts' content item.
Offers work with rules as well. There can be automatically-added offers that are added to an order based on some rules, as well as code-entered (or both at the same time). For the scenarios that you described, you probably want to show the ad based on some rules which shows up a code. Then you could create an offer that is not automatically considered and has to be retrieved by a code, but still has to have a specific set of rules in the order for it to be applied.