Changing footers in Drip Emails?

Has anyone come up with a clever solution to have just one footer which is inserted into every email (rather than editing every email)? For example, if you have set up a weekly drip email (52 emails in total for the year) but wanted to change the footer on all emails regardless of which drip number the subscriber was on, has anyone done this (maybe using tags?). An example of how this would be useful in practice is you have an event happening this week that you want to tell every subscriber about.