The technically “correct” way to do this is to create alternate master pages that include text frames at the bottom, and assign them, as needed, once you are in the final stages of doing layout, and then add the appropriate footnote text to the affected pages when all is said and done. All of that out of the way, I use Dan’s method. It’s much simpler and quicker.
A few of us have requested a “footer” option, not dissimilar to flow headings, that would dynamically affect the score as needed. Something like that would be perfect for these scenarios, especially if you could toggle the footer to be at the bottom of the page, or the end of the flow, depending on your needs (and have multiple footers).