I think it was stated that you can add song by song to an existing playlist.

"Assuming the bug is fixed, here is what you'd do. Let's assume you're already playing a playlist of only "Beatles" tracks (whether it's a pre-created "Beatles" playlist or whether it was done with a "Search By Artist" doesn't matter). Go into the "Search by Artist" feature and hit the "CD-MD CH" button to switch it from "Search By Artist" to "Append By Artist". Locate "Talk Show" and hit DNPP. Bam- you've now got a combined Beatles/TalkShow playlist playing. Right now, when I tried it, it induced the bug, but the bug is really minor: it just interrupts the current song, reshuffles the playlist, and plays a random song from the middle of the playlist. But the contents of the playlist are correct now. In my case I started a "Yes" playlist, then added all of my "Aimee Mann" tracks to it. It's now shuffling Aimee Mann songs with Yes songs. An odd combination, but hey, the feature works."