I have poked around (and prodded) the three-dots menus in the new Google Play Music UI (app version 5.x) and, for the sake of all that is free storage space, it appears to only allow managing on-device/offline tracks on a group basis, e.g. by album. Not only can I not figure out how to pin only specific, individual tracks to my Nexus 4 (without resorting to hacks like pinning a playlist and managing it that way), but I also cannot find a way to remove a single track that has pinned itself to my device without waiting for the entire album to download just so I can unpin it.
Reading the official help page on offline listening was of no help, because I simply cannot find the pin icons described in the article.
Am I just thick? Or did Google decide that storage space on the Nexus 4 isn't scant enough and needs to be filled with even more unwanted music tracks?