I don't really want to perform add/drop transaction in the add-on. The main reason is that I don't want yahoo (or others) to complain that I am taking page views from them. Giving the user the chance to review the transaction is also a plus.
Has Yahoo actually complained? I heard that they were opening an API for their fantasy sports products.
No complaints from anyone yet. but better safe than sorry. Yes the Yahoo APIs are coming soon, but it will be a long time until the other game providers follow...