How do I use iTunes' "Download Later" feature?
Ok, the problem here is that I have actually been looking for something in the iTunes application UI to do this. Rather, the solution seems to be in the web pages served by the iTunes Store.


Go to the iTunes Store.
Scroll to the bottom of the page.
Under "Features", choose "Purchased"
Choose the media type you want (it may help to choose "Not on this computer").
Click the iCloud icon to (re-)download it.